Methods for hydrothermal digestion of cellulosic biomass solids in the presence of a slurry catalyst and a digestible filter aid

ABSTRACT

Digesting cellulosic biomass in the presence of a slurry catalyst may reduce degradation product formation, but catalyst distribution and retention can be problematic. Digestion methods can comprise: providing cellulosic biomass solids and a slurry catalyst capable of activating molecular hydrogen in a digestion unit; providing a digestible filter aid in the digestion unit; distributing the slurry catalyst within the cellulosic biomass solids using fluid flow; retaining at least a portion of the slurry catalyst in a fixed location using the digestible filter aid; heating the cellulosic biomass solids in the presence of the slurry catalyst, a digestion solvent, and molecular hydrogen, thereby forming a liquor phase comprising soluble carbohydrates; and performing a catalytic reduction reaction on the soluble carbohydrates within the digestion unit, thereby at least partially forming a reaction product comprising a triol, a diol, a monohydric alcohol, or any combination thereof in the digestion unit.

CROSS-REFERENCE TO RELATED APPLICATION

This present application claims the benefit of U.S. Patent ApplicationNo. 61/665,727, filed Jun. 28, 2012, the entire disclosure of which ishereby incorporated by reference.

FIELD OF THE INVENTION

The present disclosure generally relates to digestion, and, morespecifically, to methods for retaining a slurry catalyst in a desiredlocation while digesting cellulosic biomass solids.

BACKGROUND OF THE INVENTION

A number of substances of commercial significance may be produced fromnatural sources, including biomass. Cellulosic biomass may beparticularly advantageous in this regard due to the versatility of theabundant carbohydrates found therein in various forms. As used herein,the term “cellulosic biomass” refers to a living or recently livingbiological material that contains cellulose. The lignocellulosicmaterial found in the cell walls of higher plants is the world's largestsource of carbohydrates. Materials commonly produced from cellulosicbiomass may include, for example, paper and pulpwood via partialdigestion, and bioethanol by fermentation.

Plant cell walls are divided into two sections: primary cell walls andsecondary cell walls. The primary cell wall provides structural supportfor expanding cells and contains three major polysaccharides (cellulose,pectin, and hemicellulose) and one group of glycoproteins. The secondarycell wall, which is produced after the cell has finished growing, alsocontains polysaccharides and is strengthened through polymeric ligninthat is covalently crosslinked to hemicellulose. Hemicellulose andpectin are typically found in abundance, but cellulose is thepredominant polysaccharide and the most abundant source ofcarbohydrates. The complex mixture of constituents that is co-presentwith the cellulose can make its processing difficult, as discussedhereinafter.

Significant attention has been placed on developing fossil fuelalternatives derived from renewable resources. Cellulosic biomass hasgarnered particular attention in this regard due to its abundance andthe versatility of the various constituents found therein, particularlycellulose and other carbohydrates. Despite promise and intense interest,the development and implementation of bio-based fuel technology has beenslow. Existing technologies have heretofore produced fuels having a lowenergy density (e.g., bioethanol) and/or that are not fully compatiblewith existing engine designs and transportation infrastructure (e.g.,methanol, biodiesel, Fischer-Tropsch diesel, hydrogen, and methane). Anenergy- and cost-efficient process for processing cellulosic biomassinto fuel blends having similar compositions to fossil fuels would behighly desirable to address the foregoing issues and others.

When converting cellulosic biomass into fuel blends and other materials,cellulose and other complex carbohydrates therein can be extracted andtransformed into simpler organic molecules, which can be furtherreformed thereafter. Fermentation is one process whereby complexcarbohydrates from biomass may be converted into a more usable form.However, fermentation processes are typically slow, require large volumereactors, and produce an initial reaction product having a low energydensity (ethanol). Digestion is another way in which cellulose and othercomplex carbohydrates may be converted into a more usable form.Digestion processes can break down cellulose and other complexcarbohydrates within cellulosic biomass into simpler, solublecarbohydrates that are suitable for further transformation throughdownstream reforming reactions. As used herein, the term “solublecarbohydrates” refers to monosaccharides or polysaccharides that becomesolubilized in a digestion process. Although the underlying chemistry isunderstood behind digesting cellulose and other complex carbohydratesand further transforming simple carbohydrates into organic compoundsreminiscent of those present in fossil fuels, high-yield andenergy-efficient digestion processes suitable for converting cellulosicbiomass into fuel blends have yet to be developed. In this regard, themost basic requirement associated with converting cellulosic biomassinto fuel blends using digestion and other processes is that the energyinput needed to bring about the conversion should not be greater thanthe available energy output of the product fuel blends. This basicrequirement leads to a number of secondary issues that collectivelypresent an immense engineering challenge that has not been solvedheretofore.

The issues associated with converting cellulosic biomass into fuelblends in an energy- and cost-efficient manner using digestion are notonly complex, but they are entirely different than those that areencountered in the digestion processes commonly used in the paper andpulpwood industry. Since the intent of cellulosic biomass digestion inthe paper and pulpwood industry is to retain a solid material (e.g.,wood pulp), incomplete digestion is usually performed at lowtemperatures (e.g., less than about 100° C.) for a fairly short periodof time. In contrast, digestion processes suitable for convertingcellulosic biomass into fuel blends and other materials are ideallyconfigured to maximize yields by solubilizing as much of the originalcellulosic biomass charge as possible in a high-throughput manner.

Production of greater quantities of soluble carbohydrates for use infuel blends and other materials via routine modification of paper andpulpwood digestion processes is not feasible for a number of reasons.Simply running the digestion processes of the paper and pulpwoodindustry for a longer period of time to produce more solublecarbohydrates is undesirable from a throughput standpoint. Use ofdigestion promoters such as strong alkalis, strong acids, or sulfites toaccelerate the digestion rate can increase process costs and complexitydue to post-processing separation steps and the possible need to protectdownstream components from these agents. Accelerating the digestion rateby increasing the digestion temperature can actually reduce yields dueto thermal degradation of soluble carbohydrates that can occur atelevated digestion temperatures, particularly over extended periods oftime. Once produced by digestion, soluble carbohydrates are veryreactive and can rapidly degrade to produce caramelans and other heavyends degradation products, especially under higher temperatureconditions, such as above about 150° C. Use of higher digestiontemperatures can also be undesirable from an energy efficiencystandpoint. Any of these difficulties can defeat the economic viabilityof fuel blends derived from cellulosic biomass.

One way in which soluble carbohydrates can be protected from thermaldegradation is through subjecting them to one or more catalyticreduction reactions, which may include hydrogenation and/orhydrogenolysis reactions. Stabilizing soluble carbohydrates throughconducting one or more catalytic reduction reactions may allow digestionof cellulosic biomass to take place at higher temperatures than wouldotherwise be possible without unduly sacrificing yields. Reactionproducts comprising triols, diols, monohydric alcohols, and anycombination thereof may be produced as a result of performing one ormore catalytic reduction reactions on soluble carbohydrates. Thesereaction products may be readily transformable into fuel blends andother materials through downstream reforming reactions. In addition, theabove reaction products are good solvents in which a hydrothermaldigestion may be performed. Use of such solvents, which may includemonohydric alcohols, glycols, and ketones, for example, may acceleratedigestion rates and aid in stabilizing other components of cellulosicbiomass, such as lignins, for example, which can otherwise agglomerateand foul process equipment. Separation and recycle of a solvent cansometimes require input of extensive amounts of energy, which can reducethe net energy output available from fuel blends derived from cellulosicbiomass. By using the reaction product as a solvent, the net energyoutput of the fuel blends may be increased due to a reduced need forseparation steps to take place.

Another issue associated with the processing of cellulosic biomass intofuel blends and other materials is created by the need for highconversion percentages of a cellulosic biomass charge into solublecarbohydrates. As cellulosic biomass solids are digested, their sizegradually decreases to the point that they can become fluidly mobile. Asused herein, cellulosic biomass solids that are fluidly mobile,particularly cellulosic biomass solids that are about 3 mm or less insize, will be referred to as “cellulosic biomass fines.” Unless retainedin some manner, such as through use of a screen, filter, or likeretention mechanism, cellulosic biomass fines can be fluidly transportedout of a system's digestion zone and into one or more zones where solidsare unwanted and can be detrimental. For example, cellulosic biomassfines have the potential to plug catalyst beds, transfer lines, and thelike. Even when utilizing a screen, filter, or like retention mechanism,cellulosic biomass fines may eventually become so small that they passthrough the openings therein. Although small in size, cellulosic biomassfines may represent a non-trivial fraction of the cellulosic biomasscharge, and if they are not digested and further converted into areaction product, the ability to attain a satisfactory yield may becompromised. Since the digestion processes of the paper and pulpwoodindustry are run at relatively low cellulosic biomass conversionpercentages, smaller amounts of cellulosic biomass fines are believed tobe generated and have a lesser impact on those digestion processes.

In addition to the desired carbohydrates, other substances may bepresent within cellulosic biomass that can be especially problematic todeal with in an energy- and cost-efficient manner. Sulfur- and/ornitrogen-containing amino acids or other catalyst poisons may be presentin cellulosic biomass. If not removed, these catalyst poisons can impactthe catalytic reduction reaction(s) used to stabilize solublecarbohydrates, thereby resulting in process downtime for catalystregeneration and/or replacement and reducing the overall energyefficiency when restarting the process. On the other hand, in-processremoval of these catalyst poisons can also impact the energy efficiencyof the biomass conversion process, since the ion-exchange processestypically needed to affect their removal are usually conducted attemperatures below those at which soluble carbohydrates are produced bydigestion, thereby introducing heat exchange operations that add todesign complexity and may increase operational costs. In addition tocatalyst poisons, lignin, which is a non-cellulosic biopolymer, maybecome solubilized in conjunction with the production of solublecarbohydrates. If not addressed in some manner, lignin concentrationsmay become sufficiently high during biomass conversion thatprecipitation eventually occurs, thereby resulting in costly systemdowntime. In the alternative, some lignin may remain unsolubilized, andcostly system downtime may eventually be needed to affect its removal.

As evidenced by the foregoing, the efficient conversion of cellulosicbiomass into fuel blends is a complex problem that presents immenseengineering challenges. The present disclosure addresses thesechallenges and provides related advantages as well.

SUMMARY OF THE INVENTION

The present disclosure generally relates to digestion, and, morespecifically, to methods for retaining a slurry catalyst in a desiredlocation while digesting cellulosic biomass solids.

In some embodiments, the present disclosure provides methods comprising:providing cellulosic biomass solids and a slurry catalyst in ahydrothermal digestion unit, the slurry catalyst being capable ofactivating molecular hydrogen (“Molecular Hydrogen Activating SlurryCatalyst”); providing a digestible filter aid in the hydrothermaldigestion unit; distributing the slurry catalyst within the cellulosicbiomass solids using fluid flow; retaining at least a portion of theslurry catalyst in a fixed location using the digestible filter aid;heating the cellulosic biomass solids in the hydrothermal digestion unitin the presence of the slurry catalyst, a digestion solvent, andmolecular hydrogen, thereby forming a liquor phase comprising solublecarbohydrates; and performing a first catalytic reduction reaction onthe soluble carbohydrates within the hydrothermal digestion unit,thereby at least partially forming a reaction product comprising atriol, a diol, a monohydric alcohol, or any combination thereof in thehydrothermal digestion unit.

In some embodiments, the present disclosure provides methods comprising:providing cellulosic biomass solids and a slurry catalyst in ahydrothermal digestion unit, the slurry catalyst being capable ofactivating molecular hydrogen (“Molecular Hydrogen Activating SlurryCatalyst”) and the cellulosic biomass solids comprising a digestiblefilter aid comprising cellulosic biomass particulates capable of forminga filter cake suitable for retaining at least a portion of the slurrycatalyst thereon; distributing the slurry catalyst within the cellulosicbiomass solids using upwardly directed fluid flow; heating thecellulosic biomass solids in the hydrothermal digestion unit in thepresence of the slurry catalyst, a digestion solvent, and molecularhydrogen, thereby forming a liquor phase comprising solublecarbohydrates; allowing a portion of the liquor phase to exit thehydrothermal digestion unit; forming a filter cake comprising thedigestible filter aid on a solids retention mechanism configured toallow the liquor phase to pass therethrough; collecting at least aportion of the slurry catalyst on the filter cake; and performing afirst catalytic reduction reaction on the soluble carbohydrates withinthe hydrothermal digestion unit, thereby at least partially forming areaction product comprising a triol, a diol, a monohydric alcohol, orany combination thereof in the hydrothermal digestion unit.

The features and advantages of the present disclosure will be readilyapparent to one having ordinary skill in the art upon a reading of thedescription of the embodiments that follows.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure generally relates to digestion, and, morespecifically, to methods for retaining a slurry catalyst in a desiredlocation while digesting cellulosic biomass solids.

In the embodiments described herein, the digestion rate of cellulosicbiomass solids may be accelerated in the presence of a digestionsolvent. In some instances, the digestion solvent may be maintained atelevated pressures that keep the digestion solvent in a liquid stateabove its normal boiling point. Although the more rapid digestion rateof cellulosic biomass solids under these types of conditions may bedesirable from the standpoint of throughput, soluble carbohydrates maybe susceptible to degradation at elevated temperatures, as discussedabove.

To combat the problems associated with degradation of solublecarbohydrates, the present disclosure provides methods for digestingcellulosic biomass solids while effectively promoting the thermalstabilization of soluble carbohydrates produced therefrom. Specifically,the present disclosure provides methods whereby hydrothermal digestionand one or more catalytic reduction reactions take place in the samevessel. We have found that stabilization of soluble carbohydrates occursmost effectively if conducted in this manner. The foregoing may beaccomplished by including a slurry catalyst capable of activatingmolecular hydrogen within a hydrothermal digestion unit containingcellulosic biomass solids and transporting the slurry catalyst in thedigesting liquor phase to affect its distribution therein. As usedherein, the term “slurry catalyst” refers to a catalyst comprisingfluidly mobile catalyst particles that can be at least partiallysuspended in a fluid phase via gas flow, liquid flow, mechanicalagitation, or any combination thereof. The presence of the slurrycatalyst within the hydrothermal digestion unit may allow one or more insitu catalytic reduction reactions to take place therein, therebyadvantageously intercepting and transforming soluble carbohydrates intoa more stable reaction product as soon as feasible after the solublecarbohydrates form. As used herein, the term “in situ catalyticreduction reaction” refers to a catalytic reduction reaction that occursin the same vessel as a digestion process. Formation of the reactionproduct may reduce the amount of thermal decomposition that occursduring hydrothermal digestion, thereby enabling high yield conversion ofcellulosic biomass solids into a desired reaction product to take placein a timely manner.

In addition to rapidly stabilizing soluble carbohydrates as a reactionproduct, conducting one or more in situ catalytic reduction reactionsmay also be particularly advantageous from an energy efficiencystandpoint. Specifically, the hydrothermal digestion of cellulosicbiomass is an endothermic process, whereas catalytic reduction reactionsare exothermic. Thus, the excess heat generated by the in situ catalyticreduction reaction(s) may be utilized to drive the hydrothermaldigestion, thereby lowering the amount of additional heat energy inputneeded to conduct digestion. Since digestion and catalytic reductiontake place within the same vessel in the embodiments described herein,there is minimal opportunity for heat transfer loss to take place, aswould occur if the catalytic reduction reaction(s) were to be conductedin a separate location. In addition, in such a configuration, the insitu catalytic reduction reaction(s) may provide a growing supply of thereaction product within the hydrothermal digestion unit, which may serveas and/or replenish the digestion solvent. Since the reaction productand the digestion solvent may be the same, there is no express need toseparate and recycle a majority of the digestion solvent before furtherprocessing the reaction product downstream, which may be furtheradvantageous from an energy efficiency standpoint, as discussed above.

Although conducting one or more in situ catalytic reduction reactionsmay be particularly advantageous from an energy efficiency standpointand for purposes of stabilizing soluble carbohydrates, successfullyexecuting such a coupled process may be problematic in other aspects.One significant issue that may be encountered is that of catalystdistribution within the digesting cellulosic biomass solids. Withoutadequate catalyst distribution being realized, ineffective stabilizationof soluble carbohydrates may occur. Specifically, soluble carbohydratesmay have a greater opportunity to thermally degrade during the time theytake to reach a catalytic site and undergo catalytic reduction. Incontrast, by having a well distributed catalyst, the solublecarbohydrates produced during digestion may be less removed from acatalytic site and can be stabilized more readily. Although a catalystmight be pre-mixed with cellulosic biomass solids or co-blended withcellulosic biomass solids being added to a hydrothermal digestion unit,these solutions may produce inadequate catalyst distribution and presentsignificant engineering challenges that markedly increase processcomplexity and operational costs.

In the methods described herein, a slurry catalyst may be distributedwithin cellulosic biomass solids using fluid flow to convey the slurrycatalyst therein. Although the slurry catalyst may be conveyed into thecellulosic biomass solids using fluid flow from any direction within thehydrothermal digestion unit, we consider it most effective to utilizeupwardly directed fluid flow to convey the slurry catalyst into thecellulosic biomass solids. Conveying the slurry catalyst into acellulosic biomass charge from bottom to top using upwardly directedfluid flow may present a number of advantages. Specifically, it mayovercome settling and gravity-induced compaction that occurs during theaddition and digestion of cellulosic biomass solids. Sewing andcompaction of cellulosic biomass solids may impact fluid flow throughthe hydrothermal digestion unit and particularly reduce one's ability toeffectively distribute a slurry catalyst therein. By using upwardlydirected fluid flow, settling and compaction issues may be reducedthrough promoting expansion of the cellulosic biomass charge to allowthe slurry catalyst to become distributed therein. In addition, by usingupwardly directed fluid flow, there may be a reduced need to usemechanical stirring or like means of mechanical agitation that mightotherwise be needed to obtain an adequate catalyst distribution. Thisfeature may allow high loadings of cellulosic biomass solids relative todigestion solvent to be used, thereby improving throughput and processeconomics.

Use of upwardly directed fluid flow to distribute a slurry catalystwithin cellulosic biomass solids may allow higher loadings of cellulosicbiomass solids relative to digestion solvent to be used than wouldotherwise be possible with other modes of catalyst distribution. Therelatively large size of most cellulosic biomass solids (e.g., about 1mm or greater) may produce interstitial voids within a packed orexpanded bed of cellulosic biomass solids in which a slurry catalyst maybe distributed even at high ratios of cellulosic biomass solids relativeto the digestion solvent. At high ratios of cellulosic biomass solidsrelative to digestion solvent (e.g., about 10% cellulosic biomass solidsrelative to solvent or greater), a viscous paste can form, particularlywhen the biomass particulate size is small, which may be difficult tomechanically stir or otherwise mechanically agitate. The embodimentsdescribed herein take advantage of the natural bed porosity ofcellulosic biomass solids in order to distribute a slurry catalysttherein without the need for mechanical stirring or like mixing. Theability to utilize high loadings of cellulosic biomass solids relativeto digestion solvent in the present embodiments may be advantageous froma throughput standpoint. Specifically, larger amounts of cellulosicbiomass solids may be processed per unit size of the hydrothermaldigestion unit, thereby improving process economics. Further, smallervolume digestion units, which may be simpler to construct and maintain,may also be used without sacrificing throughput, thereby further aidingprocess economics.

As one of ordinary skill in the art will recognize, retention of aslurry catalyst in a defined location is a common problem that can beencountered when using these types of catalysts. Specifically, a finelydivided slurry catalyst may flow with a fluid and be difficult toseparate via gravity sewing alone. One solution to this problem isdescribed in commonly owned U.S. Patent Application 61/665,627, filedJun. 28, 2012 entitled “Methods for Hydrothermal Digestion of CellulosicBiomass Solids in the Presence of a Distributed Slurry Catalyst,” filedconcurrently herewith and incorporated herein by reference in itsentirety. Specifically, as described therein, a slurry catalyst may berecirculated through a cellulosic biomass charge in order to distributethe catalyst therein. Recirculating the slurry catalyst may also atleast partially address the issue of cellulosic biomass fines, which mayco-circulate with the slurry catalyst in some embodiments. There is noneed to separate the slurry catalyst from the circulating fluid streamin this case, since an intent of this process is the direct return ofthe slurry catalyst to the hydrothermal digestion unit.

Although continuous recirculation of the slurry catalyst within thecellulosic biomass solids may address the issue of catalyst distributiontherein, in some instances, it may instead be more desirable to retainthe slurry catalyst in a fixed location and only perform periodicrecirculation. Continuous recirculation may also be undesirable from anenergy efficiency standpoint. As discussed below, cellulosic biomasssolids may, in some instances, effectively retain a slurry catalysttherein, such that continuous recirculation is not needed to maintaineffective catalyst distribution. In these instances and others, periodiccirculation of the slurry catalyst on an as-needed basis may besufficient to maintain good distribution of the slurry catalyst.

When the slurry catalyst is not being continuously recirculated throughthe cellulosic biomass solids, it may still be desirable to withdraw areaction product from the hydrothermal digestion unit and furthertransform the reaction product through downstream reforming reactions.As noted previously, retention of the slurry catalyst within thecellulosic biomass solids may be difficult due to its propensity totravel with a fluid stream. In many instances, it can be desirable toremove the slurry catalyst from the reaction product before conductingfurther transformations thereon. The slurry catalyst removed from thereaction product can then be returned to the hydrothermal digestionunit, if desired.

In cases where recirculation of the slurry catalyst is not performed, itmay be desirable to retain the slurry catalyst in a fixed location andonly periodically return it to the cellulosic biomass solids within thehydrothermal digestion unit. One way in which the slurry catalyst may beretained in a fixed location is through use of a filter aid. Use of afilter aid may allow buildup of a filter cake on a solids retentionmechanism, such as a grid or a filter, for example, that effectivelysequesters the slurry catalyst but allows a fluid to pass therethroughwithout inducing an excessive pressure drop. Formation of the filtercake may protect the solids retention mechanism from plugging by theslurry catalyst or other fine solids, which can result in expensivesystem downtime and capital costs for replacement, while providing areaction product that is free from the slurry catalyst. After a point intime, the filter cake may be removed from the solids retentionmechanism, and the slurry catalyst may then be redistributed in thecellulosic biomass solids using fluid flow.

We have discovered that appropriately sized cellulosic biomass solidsmay be used as a digestible filter aid to promote retention of a slurrycatalyst in a desired location during hydrothermal digestion ofcellulosic biomass solids. Specifically, such a digestible filter aidmay bridge together to form a filter cake on a solids retentionmechanism in proximity to a fluid exit of the hydrothermal digestionunit. The solids retention mechanism may reside within the hydrothermaldigestion unit or be located external to it. The solids retentionmechanism may allow solids to be removed from the reaction productexiting the hydrothermal digestion unit, such that the solids are lesslikely to result in downstream process issues. Once formed, the filtercake may at least partially sequester the slurry catalyst therein whileallowing the reaction product produced in the hydrothermal digestionunit to continue flowing therethrough. Additionally, in someembodiments, at least a portion of the digestible filter aid may bedistributed throughout the cellulosic biomass solids such that itpromotes the retention and distribution of the slurry catalyst therein.

Since the filter aid used in the embodiments described herein isdigestible, the particulates of the filter aid may eventually becomecompletely solubilized or decrease in size to the point where they nolonger form an effective filter cake on the solids retention mechanism.At this point, fluid flow through the solids retention mechanism may beimpacted, particularly if the slurry catalyst or the filter aid itselfbecomes entrained in the solids retention mechanism. Although the filteraid may sometimes be freed from the solids retention mechanism, theslurry catalyst may often not be as easily liberated. Once the filtercake is no longer functioning effectively, the filter cake may beremoved from the solids retention mechanism and returned to thecellulosic biomass solids, where the slurry catalyst on it can then bere-distributed. Although the filter cake may be removed at this point intime, it is to be recognized that it may be removed earlier, if desired,to maintain a desired filter cake thickness, to limit excessive pressuredrops across the solids retention mechanism, and/or to affect an earlierreturn of the slurry catalyst to the cellulosic biomass solids, forexample.

Once removed from the solids retention mechanism, a new filter cakeneeds to be formed. One advantage of the processes described herein isthat fresh digestible filter aid may be formed in situ during thehydrothermal digestion. Specifically, partial hydrothermal digestion ofthe cellulosic biomass solids may produce partially digested cellulosicbiomass solids, which may comprise at least some cellulosic biomassfines. At some point in the hydrothermal digestion, the cellulosicbiomass fines may become fluidly mobile and be transported to the solidsretention mechanism. Thus, as the original digestible filter aid becomesdepleted, it may be continually replaced with partially digestedcellulosic biomass solids that are generated in situ. In essence, theembodiments described herein have turned the problematic formation ofcellulosic biomass fines into a useful feature for retaining the slurrycatalyst in a desired location. Although digestible filter aid is beingproduced internally in the embodiments described herein, it is to berecognized that the digestible filter aid may, in some embodiments, besupplemented with additional digestible filter aid from an externalsource. For example, in some embodiments, after removal of the filtercake, it may be desirable to provide a fresh supply of digestible filteraid in proximity to the solids retention mechanism so as to promote morerapid formation of a new filter cake. Use of an external source of thedigestible filter aid may also allow the filter aid structure andparticulate size to be better controlled, thereby promoting optimizationof its filtration performance and minimizing the pressure drop acrossit.

Although a non-digestible filter aid could be used, at least inprinciple, to form a filter cake and promote retention of the slurrycatalyst, it may be undesirable to do so, particularly for a continuallyoperating process. Specifically, if fresh non-digestible filter aid wereto be added each time a new filter cake was deposited, quantities of thenon-digestible filter aid may eventually build to problematic levels andundesirably shorten the time period between process maintenanceoperations. For example, excessive quantities of a non-digestible filteraid may result in decreased porosity within the cellulosic biomasscharge, thereby making it increasingly difficult to distribute theslurry catalyst therein. In addition, excessive filter aid may lead tothe formation of such a voluminous filter cake that large pressure dropsoccur and fluid flow is unduly impacted. Still further, a continuallyincreasing concentration of non-digestible filter aid may requireadditional mixing and energy input to maintain its distribution in afluid and prevent solids buildup in the digestion unit, either of whichmay impact the economics of the digestion process. In contrast, bydigesting existing filter aid and continually forming it anew, as in theembodiments described herein, the total amount of filter aid may be keptwithin acceptable limits so as to avoid the foregoing issues and others.

Although conducting one or more in situ catalytic reduction reactionscan be highly desirable for the purposes of stabilizing solublecarbohydrates and achieving heat integration, the catalyst poisons andother substances within cellulosic biomass may make implementing such aprocess very difficult. When conducting an in situ catalytic reductionreaction, there is no opportunity to remove catalyst poisons before theycontact the distributed slurry catalyst. One way in which this issue canbe addressed is to use a poison-tolerant slurry catalyst, some of whichare discussed hereinbelow. Another alternative is to use a slurrycatalyst that is regenerable upon exposure to conditions that can bereadily established in or near the hydrothermal digestion unit. Forexample, in some embodiments, a regenerable slurry catalyst may beregenerated through exposure to water at a temperature of at least about300° C.

Still another alternative to address the issue of catalyst poisoning isto conduct the digestion of the cellulosic biomass solids in stages.Many of the poisons that may deactivate a slurry catalyst arise fromsulfur- and nitrogen-containing compounds in the raw cellulosic biomasssolids, particularly amino acids. Sulfur- and nitrogen-containingcompounds, along with hemicellulose and lignin, may be at leastpartially removed from cellulosic biomass solids at lower digestiontemperatures than those at which cellulose produces solublecarbohydrates. By controlling the digestion temperature, a biomass pulpmay be produced that is enriched in cellulose but depleted in catalystpoisons that may undesirably affect the catalytic activity, therebyallowing hydrothermal digestion of the biomass pulp to take place with alesser impact on catalytic activity. Notably, the biomass pulp soproduced may comprise at least a portion of the digestible filter aiddescribed herein in some embodiments. For example, all or part of thecellulosic biomass solids being introduced to the hydrothermal digestionunit may be at least partially digested to remove catalyst poisons andother undesirable materials prior to conducting hydrothermal digestionand the in situ catalytic reduction reaction. Thus, in some embodiments,the digestible filter aid may be preformed in the cellulosic biomasssolids prior to their introduction to the hydrothermal digestion unit.In some embodiments, digestible filter aid may be formed by milling orotherwise reducing the cellulosic biomass solids in size.

Unless otherwise specified herein, it is to be understood that use ofthe terms “biomass” or “cellulosic biomass” in the description hereinrefers to “cellulosic biomass solids.” Solids may be in any size, shape,or form. The cellulosic biomass solids may be natively present in any ofthese solid sizes, shapes, or forms, or they may be further processedprior to hydrothermal digestion. In some embodiments, the cellulosicbiomass solids may be chopped, ground, shredded, pulverized, and thelike to produce a desired size prior to hydrothermal digestion. In someembodiments, at least a portion of the cellulosic biomass solidsintroduced to the hydrothermal digestion unit may be of a size suitableto serve as a digestible filter aid, which may promote sequestration ofthe slurry catalyst. In some embodiments, cellulosic biomass solidsserving as the digestible filter aid may be natively present in the bulkcellulosic biomass solids. In some or other embodiments, cellulosicbiomass solids serving as the digestible filter aid may be blended withthe bulk cellulosic biomass solids. In some or other embodiments, thecellulosic biomass solids may be washed (e.g., with water, an acid, abase, combinations thereof, and the like) prior to hydrothermaldigestion taking place.

In practicing the present embodiments, any type of suitable cellulosicbiomass source may be used. Suitable cellulosic biomass sources mayinclude, for example, forestry residues, agricultural residues,herbaceous material, municipal solid wastes, waste and recycled paper,pulp and paper mill residues, and any combination thereof. Thus, in someembodiments, a suitable cellulosic biomass may include, for example,corn stover, straw, bagasse, miscanthus, sorghum residue, switch grass,bamboo, water hyacinth, hardwood, hardwood chips, hardwood pulp,softwood, softwood chips, softwood pulp, and any combination thereof.Leaves, roots, seeds, stalks, husks, and the like may be used as asource of the cellulosic biomass. Common sources of cellulosic biomassmay include, for example, agricultural wastes (e.g., corn stalks, straw,seed hulls, sugarcane leavings, nut shells, and the like), woodmaterials (e.g., wood or bark, sawdust, timber slash, mill scrap, andthe like), municipal waste (e.g., waste paper, yard clippings or debris,and the like), and energy crops (e.g., poplars, willows, switch grass,alfalfa, prairie bluestream, corn, soybeans, and the like). Thecellulosic biomass may be chosen based upon considerations such as, forexample, cellulose and/or hemicellulose content, lignin content, growingtime/season, growing location/transportation cost, growing costs,harvesting costs, and the like.

Illustrative carbohydrates that may be present in cellulosic biomasssolids include, for example, sugars, sugar alcohols, celluloses,lignocelluloses, hemicelluloses, and any combination thereof. Oncesoluble carbohydrates have been produced through hydrothermal digestionaccording to the embodiments described herein, the soluble carbohydratesmay be transformed into a more stable reaction product comprising atriol, a diol, a monohydric alcohol, or any combination thereof via oneor more catalytic reduction reactions. In some embodiments, the reactionproduct may be further reformed into a biofuel using any combination offurther hydrogenolysis reactions and/or hydrogenation reactions,condensation reactions, isomerization reactions, oligomerizationreactions, hydrotreating reactions, alkylation reactions, and the like.

In some embodiments, methods described herein can comprise: providingcellulosic biomass solids and a slurry catalyst in a hydrothermaldigestion unit, the slurry catalyst being capable of activatingmolecular hydrogen (“Molecular Hydrogen Activating Slurry Catalyst”);providing a digestible filter aid in the hydrothermal digestion unit;distributing the slurry catalyst within the cellulosic biomass solidsusing fluid flow; retaining at least a portion of the slurry catalyst ina fixed location using the digestible filter aid; heating the cellulosicbiomass solids in the hydrothermal digestion unit in the presence of theslurry catalyst, a digestion solvent, and molecular hydrogen, therebyforming a liquor phase comprising soluble carbohydrates; and performinga first catalytic reduction reaction on the soluble carbohydrates withinthe hydrothermal digestion unit, thereby at least partially forming areaction product comprising a triol, a diol, a monohydric alcohol, orany combination thereof in the hydrothermal digestion unit.

In some embodiments, methods described herein can comprise: providingcellulosic biomass solids and a slurry catalyst in a hydrothermaldigestion unit, the slurry catalyst being capable of activatingmolecular hydrogen (“Molecular Hydrogen Activating Slurry Catalyst”) andthe cellulosic biomass solids comprising a digestible filter aidcomprising cellulosic biomass particulates capable of forming a filtercake suitable for retaining at least a portion of the slurry catalystthereon; distributing the slurry catalyst within the cellulosic biomasssolids using upwardly directed fluid flow; heating the cellulosicbiomass solids in the hydrothermal digestion unit in the presence of theslurry catalyst, a digestion solvent, and molecular hydrogen, therebyforming a liquor phase comprising soluble carbohydrates; allowing aportion of the liquor phase to exit the hydrothermal digestion unit;forming a filter cake comprising the digestible filter aid on a solidsretention mechanism configured to allow the liquor phase to passtherethrough; collecting at least a portion of the slurry catalyst onthe filter cake; and performing a first catalytic reduction reaction onthe soluble carbohydrates within the hydrothermal digestion unit,thereby at least partially forming a reaction product comprising atriol, a diol, a monohydric alcohol, or any combination thereof in thehydrothermal digestion unit.

In some embodiments, heating the cellulosic biomass solids may takeplace while the hydrothermal digestion unit is in a pressurized state.As used herein, the term “pressurized state” refers to a pressure thatis greater than atmospheric pressure (1 bar). Heating a digestionsolvent in a pressurized state may allow the normal boiling point of thedigestion solvent to be exceeded, thereby allowing the rate ofhydrothermal digestion to be increased relative to lower temperaturedigestion processes. In some embodiments, heating the cellulosic biomasssolids in the hydrothermal digestion unit may take place at a pressureof at least about 30 bar. In some embodiments, heating the cellulosicbiomass solids in the hydrothermal digestion unit may take place at apressure of at least about 60 bar, or at a pressure of at least about 90bar. In some embodiments, heating the cellulosic biomass solids in thehydrothermal digestion unit may take place at a pressure ranging betweenabout 30 bar and about 430 bar. In some embodiments, heating thecellulosic biomass solids in the hydrothermal digestion unit may takeplace at a pressure ranging between about 50 bar and about 330 bar, orat a pressure ranging between about 70 bar and about 130 bar, or at apressure ranging between about 30 bar and about 130 bar.

In some embodiments, the cellulosic biomass solids may be maintained atpressure of at least about 30 bar and heated at a temperature of atleast about 150° C. In some embodiments, the cellulosic biomass solidsmay be maintained at a pressure of at least about 70 bar, or at leastabout 100 bar, and heated at a temperature of at least about 150° C. Insome or other embodiments, the cellulosic biomass solids may be heatedat a temperature of at least about 200° C., or at least about 250° C.,or at least about 300° C.

In some embodiments, the cellulosic biomass solids and the slurrycatalyst may be provided in the hydrothermal digestion unit at the sametime. For example, in some embodiments, a mixture of cellulosic biomasssolids and the slurry catalyst may be concurrently introduced to thehydrothermal digestion unit. In other embodiments, the cellulosicbiomass solids and the slurry catalyst may be added at the same time inseparate feeds to the hydrothermal digestion unit. When introduced tothe hydrothermal digestion unit at the same time as the cellulosicbiomass solids, the slurry catalyst can either be distributed in thecellulosic biomass solids or it can remain undistributed.

In some embodiments, the cellulosic biomass solids and the slurrycatalyst may be provided in the hydrothermal digestion unit separately.In some embodiments, the slurry catalyst may be provided in thehydrothermal digestion unit before the cellulosic biomass solids areprovided. For example, during process startup, the slurry catalyst maybe provided in the hydrothermal digestion unit before the cellulosicbiomass solids are provided. In some embodiments, the slurry catalystmay be placed on or near the bottom of the hydrothermal digestion unitand a charge of cellulosic biomass solids may be placed on the slurrycatalyst thereafter. Placing the slurry catalyst in the hydrothermaldigestion unit prior to the cellulosic biomass solids may position theslurry catalyst such that it can be distributed in the cellulosicbiomass solids using upwardly directed fluid flow. In some embodiments,the slurry catalyst may be present in the hydrothermal digestion unit,optionally along with partially digested cellulosic biomass solids,while fresh cellulosic biomass solids are being added thereto.

In some embodiments, the hydrothermal digestion unit may be charged witha fixed amount of slurry catalyst, while cellulosic biomass solids arecontinuously or semi-continuously fed thereto, thereby allowinghydrothermal digestion to take place in a continual manner. That is,fresh cellulosic biomass solids may be added to the hydrothermaldigestion unit on a continual or an as-needed basis in order toreplenish cellulosic biomass solids that have been digested to formsoluble carbohydrates. In some embodiments, the cellulosic biomasssolids may be continuously or semi-continuously provided to thehydrothermal digestion unit while the hydrothermal digestion unit is ina pressurized state. In some embodiments, the pressurized state maycomprise a pressure of at least about 30 bar. Without the ability tointroduce fresh cellulosic biomass to a pressurized hydrothermaldigestion unit, depressurization and cooling of the hydrothermaldigestion unit may take place during biomass addition, significantlyreducing the energy- and cost-efficiency of the biomass conversionprocess. As used herein, the term “continuous addition” and grammaticalequivalents thereof will refer to a process in which cellulosic biomasssolids are added to a hydrothermal digestion unit in an uninterruptedmanner without fully depressurizing the hydrothermal digestion unit. Asused herein, the term “semi-continuous addition” and grammaticalequivalents thereof will refer to a discontinuous, but as-needed,addition of cellulosic biomass solids to a hydrothermal digestion unitwithout fully depressurizing the hydrothermal digestion unit. Meansthrough which cellulosic biomass solids may be added continuously orsemi-continuously to a pressurized hydrothermal digestion unit arediscussed in more detail hereinbelow.

In some embodiments, cellulosic biomass solids being continuously orsemi-continuously added to the hydrothermal digestion unit may bepressurized before being added to the hydrothermal digestion unit,particularly when the hydrothermal digestion unit is in a pressurizedstate. Pressurization of the cellulosic biomass solids from atmosphericpressure to a pressurized state may take place in one or morepressurization zones before addition of the cellulosic biomass solids tothe hydrothermal digestion unit. Suitable pressurization zones that maybe used for pressurizing and introducing cellulosic biomass solids to apressurized hydrothermal digestion unit are described in more detail incommonly owned United States Patent Application Publications2013/0152457 and 2013/0152458, each filed on Dec. 20, 2011, andincorporated herein by reference in its entirety. Suitablepressurization zones described therein may include, for example,pressure vessels, pressurized screw feeders, and the like. In someembodiments, multiple pressurization zones may be connected in series toincrease the pressure of the cellulosic biomass solids in a stepwisemanner.

In some embodiments, providing the digestible filter aid in thehydrothermal digestion unit may comprise forming the digestible filteraid in the hydrothermal digestion unit by heating the cellulosic biomasssolids in the presence of the digestion solvent. That is, in suchembodiments, the digestible filter aid may be formed in situ within thehydrothermal digestion unit. In some embodiments, the methods mayfurther comprise adding an additional quantity of the digestible filteraid to the hydrothermal digestion unit while the digestible filter aidis being formed therein.

In some embodiments, providing the digestible filter aid in thehydrothermal digestion unit may comprise adding the digestible filteraid to the hydrothermal digestion unit. In some embodiments, thedigestible filter aid may be added when the cellulosic biomass solidstherein do not already contain existing cellulosic biomass particulatesor another digestible filter aid suitable for forming a filter cake. Inother embodiments, the digestible filter aid may be added to thehydrothermal digestion unit to supplement an existing quantity ofdigestible filter aid present or being produced therein.

When starting up processes described by the various methods set forthherein, it may be desirable to provide the digestible filter aid in thehydrothermal digestion unit before commencing distribution of the slurrycatalyst. In various embodiments, the digestible filter aid may be addedseparately from or together with the slurry catalyst and/or thecellulosic biomass solids. In some embodiments, the digestible filteraid may be added to the hydrothermal digestion unit with the cellulosicbiomass solids. In some embodiments, the cellulosic biomass solids maynatively contain at least some cellulosic biomass solids of a sizesuitable to promote retention of the slurry catalyst in a fixed location(e.g., through formation of a filter cake). In some or otherembodiments, the cellulosic biomass solids may be processed prior totheir introduction to the hydrothermal digestion unit such that at leasta portion of the cellulosic biomass solids have a suitable size topromote retention of the slurry catalyst in a fixed location. In some orother embodiments, separate feeds of the digestible filter aid and thecellulosic biomass solids may be introduced to the hydrothermaldigestion unit.

After starting up the process, the digestible filter aid may be producedduring hydrothermal digestion of the cellulosic biomass solids, in someembodiments. As described above, hydrothermal digestion of thecellulosic biomass solids may produce cellulosic biomass particulates ofa size suitable to serve as a digestible filter aid. In someembodiments, the cellulosic biomass particulates serving as thedigestible filter aid may comprise cellulosic biomass fines. Thedigestible filter aid being produced may replace or supplement thatoriginally present and now being consumed by hydrothermal digestion. Insome or other embodiments, additional digestible filter aid may beintroduced to the hydrothermal digestion unit to supplement thatproduced during hydrothermal digestion of the cellulosic biomass solids.

The digestible filter aid used in the present embodiments, especiallythat used for starting up the process, is not believed to beparticularly limited. In general, any material that can promoteretention of the slurry catalyst and become solubilized at a suitablerate in the digestion solvent without producing undesirable materialsthat might, for example, poison the slurry catalyst, foul thehydrothermal digestion unit, and/or interfere with downstream reformingreactions may be used as the digestible filter aid. Suitable materialsmay include, for example, thermally or hydrolytically degradablepolymers, slowly soluble organic or inorganic compounds, salts, sugars,combinations thereof, and the like. In some embodiments, the filter aidused for starting up the process may comprise a non-digestible filteraid, with digestible filter aid being produced thereafter throughdigestion of the cellulosic biomass solids. Startup use of anon-digestible filter aid is not believed to lead to problematic filteraid buildup.

In some embodiments, the digestible filter aid may be derived fromcellulosic biomass solids. In some embodiments, the digestible filteraid may comprise partially digested cellulosic biomass solids (e.g., abiomass pulp). In some embodiments, the digestible filter aid maycomprise a low valued cellulosic material such as, for example, sawdust,milled straws, shredded paper, and the like. In some or otherembodiments, the digestible filter aid may comprise cellulosic biomassfines. In some embodiments, the biomass pulp and/or cellulosic biomassfines may be formed external to the hydrothermal digestion unit andadded thereto (e.g., during process startup and/or to supplementdigestible filter aid formed during hydrothermal digestion). Forming adigestible filter aid from cellulosic biomass external to thehydrothermal digestion unit may be advantageous from the standpoint oflimiting the introduction of catalyst poisons and other undesirablematerials to the hydrothermal digestion unit. In some or otherembodiments, after process startup, formation of the digestible filteraid may take place in situ within the hydrothermal digestion unit whilehydrothermal digestion of the cellulosic biomass solids takes place.

In some embodiments, cellulosic biomass solids comprising the digestiblefilter aid may have a particulate size of at most about 5 mm. In otherembodiments, cellulosic biomass solids comprising the digestible filteraid may have a particulate size of at most about 4 mm, or at most about3 mm, or at most about 2 mm, or at most about 1 mm, or at most about 900μm, or at most about 800 μm, or at most about 700 μm, or at most about600 μm, or at most about 500 μm, or at or at most about 400 μm, or atmost about 300 μm, or at most about 200 μm, or at most about 100 μm. Insome embodiments, the cellulosic biomass solids comprising thedigestible filter aid may have a particulate size ranging between 3 mmand about 10 μm or between about 100 μm and about 10 μm. Generally, thelargest particulate size suitable for forming a filter cake will bedetermined by a pore size present in the solids retention mechanism. Insome embodiments, the digestible filter aid may comprise a plurality ofparticulate sizes. Use of a filter aid comprising a variety ofparticulate sizes may promote formation of a more robust filter cake. Insome embodiments, the cellulosic biomass solids comprising thedigestible filter aid may comprise cellulosic biomass fines.Specifically, in some embodiments, the digestible filter aid maycomprise cellulosic biomass particulates with a particulate size of atmost about 3 mm that are formed by heating the cellulosic biomass solidsin the presence of the digestion solvent.

In various embodiments described herein, upwardly directed fluid flowmay be used to distribute the slurry catalyst within cellulosic biomasssolids. As used herein, the terms “distribute,” “distribution,” andvariants thereof refer to a condition in which a slurry catalyst isspread along at least a portion of the height of a cellulosic biomasscharge and not all concentrated in one location. No particular degree ofdistribution is implied by use of the term “distribute” or its variants.In some embodiments, the slurry catalyst may be distributed throughoutthe height of the cellulosic biomass charge. In other embodiments, theslurry catalyst may be distributed throughout only a portion of thecellulosic biomass charge. In some embodiments, the distribution maycomprise a substantially homogeneous distribution, such that aconcentration of the slurry catalyst is substantially the same at allheights of a cellulosic biomass charge. In other embodiments, thedistribution may comprise a heterogeneous distribution, such thatdifferent concentrations of the slurry catalyst are present at differentheights of the cellulosic biomass charge. When a heterogeneousdistribution of the slurry catalyst is present, a concentration of theslurry catalyst within the cellulosic biomass solids may increase fromtop to bottom in some embodiments or decrease from top to bottom inother embodiments. In some embodiments, the upwardly directed fluid flowvelocity may be used to modulate the type of slurry catalystdistribution obtained.

In some embodiments, the upwardly directed fluid flow may commencebefore heating of the cellulosic biomass solids commences. Specifically,in some embodiments, distributing the slurry catalyst may take placebefore forming a liquor phase comprising soluble carbohydrates. In otherembodiments, heating of the cellulosic biomass solids may commencebefore the upwardly directed fluid flow commences. Although it isgenerally desirable to distribute the slurry catalyst within thecellulosic biomass solids before production of soluble carbohydratesoccurs, some degree of heating prior to slurry catalyst distribution maybe tolerable in some embodiments. For example, if desired, thecellulosic biomass solids may first be heated at a temperature that isnot sufficient to produce and/or degrade soluble carbohydrates beforecommencing upwardly directed fluid flow to distribute the slurrycatalyst. Reasons why one might heat the cellulosic biomass solids at atemperature below that at which soluble carbohydrates are produced mayinclude, for example, removal of non-cellulosic materials, includingcatalyst poisons, from the cellulosic biomass. In addition, since thehydrothermal digestion processes described herein may take placecontinuously, in some embodiments, the slurry catalyst may becomedistributed in fresh cellulosic biomass solids being charged to thehydrothermal digestion unit while hydrothermal digestion and solublecarbohydrate formation continues in the cellulosic biomass solidsalready present therein.

In various embodiments, the upwardly directed fluid flow may compriseone or more upwardly directed fluid streams. In various embodiments, theone or more upwardly directed fluid streams may pass through thecellulosic biomass solids, carrying the slurry catalyst thereto, and theone or more upwardly directed fluid streams may subsequently exit thehydrothermal digestion unit. In some embodiments, the upwardly directedfluid flow may comprise one upwardly directed fluid stream. In someembodiments, the upwardly directed fluid flow may comprise two upwardlydirected fluid streams, or three upwardly directed fluid streams, orfour upwardly directed fluid streams, or five upwardly directed fluidstreams. In some embodiments, the one or more upwardly directed fluidstreams may comprise a gas stream, a liquid stream, or any combinationthereof.

In some embodiments, the upwardly directed fluid stream may comprise agas stream. For example, in some embodiments, a gas stream being usedfor upwardly directed fluid flow may comprise a stream of molecularhydrogen. In some or other embodiments, steam, compressed air, or aninert gas such as nitrogen, for example, may be used in place of or inaddition to a stream of molecular hydrogen. Up to about 40% steam may bepresent in the fluid stream in various embodiments. While a gas streammay carry the slurry catalyst through the cellulosic biomass solids,progression of the slurry catalyst within the hydrothermal digestionunit is generally capped by the liquid level therein. That is, underordinary circumstances a gas stream is generally not sufficient to carrythe slurry catalyst out of the hydrothermal digestion unit.

In some embodiments, the upwardly directed fluid stream may comprise aliquid stream. Unlike a gas stream, described above, a liquid streammay, in some embodiments, carry the slurry catalyst through thecellulosic biomass solids and potentially out of the hydrothermaldigestion unit, since the liquid stream adds to the liquid leveltherein. Liquid exiting the hydrothermal digestion unit may carry theslurry catalyst with it. As described herein, it can be desirable tosequester the slurry catalyst prior to or after its exit from thehydrothermal digestion unit and eventually recycle the slurry catalystto the cellulosic biomass solids. In some embodiments, the liquid streammay comprise a stream of the digestion solvent. In some embodiments, thedigestion solvent may comprise the reaction product formed in thehydrothermal digestion unit.

In some embodiments, the methods described herein may further compriseretaining the cellulosic biomass solids in the hydrothermal digestionunit through use of a retention structure. The retention structure mayallow digestion solvent, filter aid, slurry catalyst, and other types ofsmall particulates to pass through but may lack sufficient porosity toallow bulk cellulosic biomass solids from passing through. Use of aretention structure may be beneficial, for example, when upwardlydirected fluid flow used for distributing the slurry catalyst undulyfluidizes the cellulosic biomass solids. Use of the retention structuremay allow a fluid exit from the hydrothermal digestion unit to remainunblocked by bulk cellulosic biomass solids, for example. Suitableretention structures may include, for example, a screen or likegrid-like structure, a frit (e.g., a metal or glass frit), a filter, amat, a porous plate, or the like.

In some embodiments, the methods described herein may further compriseallowing a portion of the liquor phase to exit the hydrothermaldigestion unit, forming a filter cake comprising the digestible filteraid on a solids retention mechanism configured to allow the liquor phaseto pass therethrough, and collecting at least a portion of the slurrycatalyst on the filter cake. In various embodiments, allowing a portionof the liquor phase to exit the hydrothermal digestion unit may compriseflowing the liquor phase from the hydrothermal digestion unit. Invarious embodiments, the solids retention mechanism may comprise ascreen or like grid-like structure, a filter, a frit, a membrane, or alike porous medium through which the liquor phase may pass.

While or after the liquor phase exits the hydrothermal digestion unit,the slurry catalyst may be removed from the liquor phase throughcollection on the filter cake. In some embodiments, the slurry catalystmay be collected and retained while remaining within the hydrothermaldigestion unit. Specifically, in some embodiments, the solids retentionmechanism may reside within the hydrothermal digestion unit. In otherembodiments, the slurry catalyst may be collected and retained externalto the hydrothermal digestion unit. Specifically, in some embodiments,the solids retention mechanism may reside external to the hydrothermaldigestion unit. For example, in some embodiments, the solids retentionmechanism may be in fluid communication with a fluid conduit exiting thehydrothermal digestion unit. Although a filter or like solids separationmechanism may be used either internal or external to the hydrothermaldigestion unit in the embodiments described herein, use of an externallylocated solids separation mechanism may be more desirable formaintenance purposes. In addition, as discussed below, a filter cakeremoved from an externally located filter may be more readily returnedto the bottom of a cellulosic biomass charge for purposes of catalystredistribution.

In some embodiments, the methods described herein may further compriseremoving the filter cake from the solids retention mechanism, andreturning at least a portion of the slurry catalyst to the cellulosicbiomass solids. In some embodiments, removing the filter cake maycomprise reversing the fluid flow through the solids retention mechanismto “blow back” the filter aid and slurry catalyst from its surface. Insome or other embodiments, removing the filter cake may compriseapplying cross-flow to the filter cake so as to affect its removal.After removal of the filter cake, in some embodiments, the methods mayfurther comprise returning at least a portion of the slurry catalyst tothe cellulosic biomass solids. In some embodiments, at least a portionof the slurry catalyst may be returned to the top of the cellulosicbiomass solids in the hydrothermal digestion unit. In some or otherembodiments, at least a portion of the slurry catalyst may be returnedto the bottom of the cellulosic biomass solids in the hydrothermaldigestion unit.

When the solids retention mechanism is located internally within thehydrothermal digestion unit, removal of the filter cake may directlyreturn the slurry catalyst to the cellulosic biomass solids. Generally,the slurry catalyst is returned near the same height at which it wascollected, and redistribution of the catalyst may take place via ongoingfluid mixing within the hydrothermal digestion unit. In contrast, whenthe solids retention mechanism is located external to the hydrothermaldigestion unit, removal of the filter cake therefrom may directly returnthe slurry catalyst to the hydrothermal digestion unit by way of thefluid pathway through which it originally travelled or by way of adifferent return pathway. Specifically, in some embodiments, when thesolids retention mechanism is external to the hydrothermal digestionunit, the filter cake may be removed therefrom, and the slurry catalystmay be routed back to the bottom of the hydrothermal digestion unit forsubsequent redistribution in the cellulosic biomass solids. Return ofthe filter cake from an external solids retention mechanism mayadvantageously promote breakup of the filter cake, thereby facilitatingthe re-distribution of slurry catalyst and filter aid once returned tothe hydrothermal digestion unit. In alternative embodiments, at least aportion of the slurry catalyst may be removed from the system. Removalmay be desirable, for example, if the slurry catalyst needs to beregenerated.

Unless measures are taken to the contrary, the solids retentionmechanism may be at the same temperature as the liquor phase passingtherethrough. Accordingly, in some embodiments, the filter cake may beat least partially digested while on the solids retention mechanism. Tomaintain the filter cake for a longer period of time, in someembodiments, it may be desirable to moderate the digestion rate of thedigestible filter aid comprising the filter cake. Specifically, in someembodiments, the solids retention mechanism may be maintained at a lowertemperature than that used during digestion so as to reduce thedigestion rate of the filter cake disposed thereon and to otherwiseprotect the solids retention mechanism. In some embodiments, the solidsretention mechanism may be maintained at a temperature of about 150° C.or below. In some embodiments, the solids retention mechanism may bemaintained at a temperature of about 140° C. or below, or about 130° C.or below, or about 120° C. or below, or about 110° C. or below, or about100° C. or below.

In some or other embodiments, it may be desirable to maintain the solidsretention mechanism at a higher temperature than that at which digestionis taking place. Although a higher temperature at the solids retentionmechanism may promote premature filter cake digestion, heating mayreduce the likelihood of precipitation of cellulosic biomass componentssuch as, for example, lignins and tars in the solids retentionmechanism.

In some embodiments, in addition to forming a filter cake, at least aportion of the digestible filter aid may be distributed within thecellulosic biomass solids, where it may promote retention of the slurrycatalyst therein. Again, no particular degree of distribution is to beimplied by use of the term “distribute.” In some embodiments, thedigestible filter aid may be homogeneously distributed in the cellulosicbiomass solids. In other embodiments, the digestible filter aid may beheterogeneously distributed in the cellulosic biomass solids. Thus, insome embodiments, the digestible filter aid may advantageously promotecatalyst retention in the cellulosic biomass solids during times whenthe catalyst is being circulated therethrough.

As described above, the methods described herein may produce additionaldigestible filter aid through in situ hydrothermal digestion of thecellulosic biomass solids so as to replace that consumed by hydrothermaldigestion. In some embodiments, the methods described herein may furthercomprise dissolving at least a portion of the digestible filter aid. Inmore specific embodiments, the methods may comprise dissolving at leasta portion of the digestible filter aid while forming fresh digestiblefilter aid, where the fresh digestible filter aid comprises cellulosicbiomass particulates with a particulate size of at most about 3 mm thatare formed by heating the cellulosic biomass solids in the presence ofthe digestion solvent.

In some embodiments, at least a portion of the slurry catalyst may befluidly suspended in the digestion solvent by the upwardly directedfluid flow. As used herein, the term “fluidly suspended” refers to thecondition that exists when the upwardly directed fluid flow velocitymatches the terminal velocity of the slurry catalyst particulates.Accordingly, fluidly suspended slurry catalyst particulates neither sinkto the bottom of the hydrothermal digestion unit nor pass completelythrough the top of a cellulosic biomass charge, carried by the upwardlydirected fluid flow. In some embodiments of the methods describedherein, a portion of the slurry catalyst may be fluidly suspended and aportion of the slurry catalyst may be transported through the cellulosicbiomass solids and subsequently collected on a filter cake formed by thedigestible filter aid. Slurry catalyst particulates may be transportedthrough the cellulosic biomass solids by the upwardly directed fluidflow if the upwardly directed fluid flow velocity exceeds the terminalvelocity of the slurry catalyst particulates. In further embodiments, aportion of the slurry catalyst may remain at the bottom of thehydrothermal digestion unit, even when another portion of the slurrycatalyst is fluidly suspended. Attaining a fluidly suspended state forthe slurry catalyst may comprise sizing the slurry catalyst particulatesto match an intended velocity of upwardly directed fluid flow, adjustingthe velocity of upwardly directed fluid flow to match the range ofparticulate sizes present in a given slurry catalyst, or any combinationthereof.

In various embodiments, the first catalytic reduction reaction performedin the hydrothermal digestion unit may take place in the presence ofmolecular hydrogen. In some embodiments, the molecular hydrogen may beexternally supplied to the hydrothermal digestion unit. For example, insome embodiments, the molecular hydrogen may be supplied with theupwardly directed fluid flow. In some or other embodiments, themolecular hydrogen may be generated internally through use of an aqueousphase reforming (APR) catalyst. Generation of molecular hydrogen usingan APR catalyst may take place within the hydrothermal digestion unit insome embodiments or externally in other embodiments.

In some embodiments, the slurry catalyst may comprise a poison-tolerantcatalyst. Use of a poison-tolerant catalyst may be particularlydesirable when catalyst poisons are not removed from the cellulosicbiomass solids before production of soluble carbohydrates takes place.As used herein, a “poison-tolerant catalyst” is defined as a catalystthat is capable of activating molecular hydrogen without needing to beregenerated or replaced due to low catalytic activity for at least about12 hours of continuous operation. Use of a poison-tolerant catalyst maylessen the disadvantages of process downtime that are associated withcatalyst regeneration/replacement and process restart.

In some embodiments, suitable poison-tolerant catalysts may include, forexample, a sulfided catalyst. In some or other embodiments, a nitridedcatalyst may be used as a poison-tolerant catalyst. Sulfided catalystssuitable for activating molecular hydrogen (Sulfided Molecular HydrogenActivating Catalysts) are described in commonly owned United StatesPatent Application Publications 2012/0317872, 2012/0317873, and2013/0109896, each of which is incorporated herein by reference in itsentirety. Sulfiding may take place by treating the catalyst withhydrogen sulfide or an alternative sulfiding agent, optionally while thecatalyst is disposed on a solid support. In more particular embodiments,the poison-tolerant catalyst may comprise a sulfided cobalt-molybdatecatalyst. We have found that sulfided cobalt-molybdate catalysts,depending on the reaction conditions, may produce C2-C6 monohydricalcohols, diols (including glycols), triols, and combinations thereof,while not forming an excessive amount of C2-C4 alkanes. As used herein,the term “monohydric alcohol” refers to an organic molecule containing asingle alcohol functional group. Monohydric alcohols formed may bereadily separated from water via flash vaporization or liquid-liquidphase separation, and undergo condensation-oligomerization reactions inseparate steps over an acid or base catalyst, to produce liquid biofuelsin the gasoline, jet, or diesel range. Slurry catalysts containing Pt orPd may also be particularly useful poison-tolerant catalysts for use inthe present embodiments.

In some embodiments, slurry catalysts suitable for use in the methodsdescribed herein may be sulfided by dispersing a slurry catalyst in afluid phase and adding a sulfiding agent thereto. Suitable sulfidingagents may include, for example, organic sulfoxides (e.g., dimethylsulfoxide), hydrogen sulfide, salts of hydrogen sulfide (e.g., NaSH),and the like. In some embodiments, the slurry catalyst may beconcentrated in the fluid phase after sulfiding and then added to thehydrothermal digestion unit.

In some embodiments, the slurry catalyst may be regenerable. Forexample, in some embodiments, the slurry catalyst may be regenerablethrough exposure to water at a temperature above its normal boilingpoint. As used herein, a “regenerable catalyst” may have at least someof its catalytic activity restored through regeneration, even whenpoisoned with nitrogen compound impurities, sulfur compound impurities,or any combination thereof. Ideally, such regenerable catalysts shouldbe regenerable with a minimal amount of process downtime. In someembodiments, the slurry catalyst may be regenerated through exposure towater having a temperature of at least about 200° C. In someembodiments, the slurry catalyst may be regenerated through exposure towater having a temperature of at least about 250° C., or at least about300° C., or at least about 350° C., or at least about 400° C. The waterused for regenerating the slurry catalyst may be in a subcritical stateor a supercritical state. A particularly suitable slurry catalyst thatcan be regenerated though exposure to water above its normal boilingpoint is ruthenium disposed on a solid support such as, for example,ruthenium on titanium dioxide or ruthenium on carbon. Other suitableslurry catalysts may include a platinum or palladium compound disposedon a solid support. Most catalysts effective for mediating a catalyticreduction reaction are also regenerable, at least in part, throughthermal treatments with hydrogen. Regeneration of the slurry catalystmay take place in the hydrothermal digestion unit or elsewhere, ifdesired.

In various embodiments, the slurry catalyst may have a particulate sizeof about 250 microns or less. In some embodiments, the slurry catalystmay have a particulate size of about 100 microns or less. In someembodiments, the slurry catalyst may have a particulate size of about 10microns or less. In some embodiments, the minimum particulate size ofthe slurry catalyst may be about 1 micron. In some embodiments, theslurry catalyst may comprise catalyst fines in the processes describedherein. As used herein, the term “catalyst fines” refers to solidcatalysts having a nominal particulate size of about 100 microns orless. Catalyst fines may be generated from catalyst productionprocesses, for example, during extrusion of solid catalyst. Catalystfines may also be produced by grinding larger catalyst solids or duringregeneration of catalyst solids. Suitable methods for producing catalystfines are described in U.S. Pat. Nos. 6,030,915 and 6,127,299, each ofwhich is incorporated herein by reference in its entirety. In someinstances, catalyst fines may be removed from a solid catalystproduction run, since they may be difficult to sequester in somecatalytic processes. Techniques for removing catalyst fines from largercatalyst solids may include, for example, sieving or like sizeseparation processes. Since there is no requirement to retain thecatalyst in a fixed location in the embodiments described herein,catalyst fines may be particularly well tolerated. Advantageously, dueto their small size, catalyst fines may be easily fluidized anddistributed throughout the cellulosic biomass solids.

In some embodiments, the slurry catalyst may be operable to generatemolecular hydrogen. For example, in some embodiments, catalysts suitablefor aqueous phase reforming (i.e., APR catalysts) may be used. SuitableAPR catalysts may include, for example, catalysts comprising platinum,palladium, ruthenium, nickel, cobalt, or other Group VIII metals alloyedor modified with rhenium, molybdenum, tin, or other metals. Thus, insome embodiments described herein, an external hydrogen feed may not beneeded. However, in other embodiments, an external hydrogen feed may beused, optionally in combination with internally generated hydrogen.

In addition to fluidizing the slurry catalyst and the digestible filteraid, the upwardly directly fluid flow may fluidize the cellulosicbiomass solids in some embodiments. In other embodiments, the upwardlydirected fluid flow does not substantially fluidize the cellulosicbiomass solids. In some embodiments, the velocity of the upwardlydirected fluid flow may be sufficient to fluidize the digestible filteraid and slurry catalyst but not the bulk cellulosic biomass solids. Oneof ordinary skill in the art will be able to choose an appropriatevelocity of the upwardly directed fluid flow suitable for a givenapplication depending on whether one desires to fluidize the cellulosicbiomass solids in combination with the slurry catalyst and digestiblefilter aid.

In some embodiments, the upwardly directed fluid flow may at leastpartially expand the cellulosic biomass solids within the hydrothermaldigestion unit. As used herein the terms “at least partially expand” and“at least partial expansion” refer to a condition in which the packingdensity of the cellulosic biomass solids is reduced by the upwardlydirected fluid flow. At least partial expansion of the cellulosicbiomass solids may be beneficial to ensure good distribution of theslurry catalyst therein and/or to reduce the likelihood of blockagesoccurring in the hydrothermal digestion unit.

In some instances it may be desirable to conduct further catalyticreduction reactions on the reaction product (e.g., triols, diols, and/ormonohydric alcohols) produced in the hydrothermal digestion unit. Forexample, it may be desirable to perform further hydrogenolysis reactionsto reduce the molecular weight of the reaction products, or it may bedesirable to affect a further reduction in the degree of oxygenation ofthe reaction product. In some embodiments, the methods described hereinmay further comprise performing a second catalytic reduction reaction onthe liquor phase that has exited the hydrothermal digestion unit so asto further form the reaction product. For example, in some embodiments,the reaction product formed in the hydrothermal digestion unit may betransferred from the hydrothermal digestion unit to a reactor configuredfor conducting a catalytic reduction reaction, where the degree ofoxygenation of the reaction product may be further lowered.Specifically, in some embodiments, the second catalytic reductionreaction may be used to increase the amount of monohydric alcoholspresent in the reaction product. In some embodiments, at least a portionof the reaction product produced in the second catalytic reductionreaction may be recirculated to the hydrothermal digestion unit.

In other embodiments, the reaction product from the hydrothermaldigestion unit may be processed directly into fuel blends withoutperforming a second catalytic reduction reaction thereon. Since theliquor phase withdrawn from the hydrothermal digestion unit has had theslurry catalyst removed therefrom, the liquor phase may be useddirectly, if desired, in such downstream reforming reactions.

When performing a second catalytic reduction reaction, the catalyst usedin the reactor may be the same or different than that used in thehydrothermal digestion unit. In some embodiments, the catalyst used forperforming the second catalytic reduction reaction may be a slurrycatalyst, which may be the same slurry catalyst used in the hydrothermaldigestion unit or a different slurry catalyst. In other embodiments, thecatalyst used for performing the second catalytic reduction reaction maybe different. In some embodiments the catalyst used for conducting thesecond catalytic reduction reaction may comprise a fixed bed catalyst,an ebullating bed catalyst, a fluidized bed catalyst, or the like.

In some embodiments, one or more separation or purification steps may beemployed after the liquor phase exits the hydrothermal digestion unit.Separation or purification steps that may be performed include, forexample, ion-exchange, flash distillation, adsorption, and the like.Thereafter, further transformation of the reaction product may takeplace.

Application of the methods described herein may allow high percentagesof a cellulosic biomass charge to be solubilized by digestion. In someembodiments, at least about 60% of the cellulosic biomass solids, on adry basis, may be digested to produce a hydrolysate comprising solublecarbohydrates. In some embodiments, at least about 70% of the cellulosicbiomass solids, on a dry basis, may be digested to produce a hydrolysatecomprising soluble carbohydrates. In some embodiments, at least about80% of the cellulosic biomass solids, on a dry basis, may be digested toproduce a hydrolysate comprising soluble carbohydrates. In someembodiments, at least about 90% of the cellulosic biomass solids, on adry basis, may be digested to produce a hydrolysate comprising solublecarbohydrates. In some embodiments, at least about 95% of the cellulosicbiomass solids, on a dry basis, may be digested to produce a hydrolysatecomprising soluble carbohydrates. In some embodiments, at least about97% of the cellulosic biomass solids, on a dry basis, may be digested toproduce a hydrolysate comprising soluble carbohydrates. In someembodiments, at least about 99% of the cellulosic biomass solids, on adry basis, may be digested to produce a hydrolysate comprising solublecarbohydrates.

In some or other embodiments, at least about 60% of the solublecarbohydrates produced by hydrothermal digestion may form a reactionproduct comprising a triol, a diol, a monohydric alcohol, or anycombination thereof. In some or other embodiments, at least about 70% ofthe soluble carbohydrates produced by hydrothermal digestion may form areaction product comprising a triol, a diol, a monohydric alcohol, orany combination thereof. In some or other embodiments, at least about80% of the soluble carbohydrates produced by hydrothermal digestion mayform a reaction product comprising a triol, a diol, a monohydricalcohol, or any combination thereof. In some or other embodiments, atleast about 90% of the soluble carbohydrates produced by hydrothermaldigestion may form a reaction product comprising a triol, a diol, amonohydric alcohol, or any combination thereof. In some or otherembodiments, at least about 95% of the soluble carbohydrates produced byhydrothermal digestion may form a reaction product comprising a triol, adiol, a monohydric alcohol, or any combination thereof.

In some embodiments, prior to hydrothermal digestion, the cellulosicbiomass solids may be washed, chemically treated, and/or reduced in size(e.g., by chopping, crushing, debarking, and the like) to achieve adesired size and quality for being digested. In some embodiments, theforegoing operations may remove substances that interfere with furtherchemical transformation of soluble carbohydrates and/or improve thepenetration of the digestion solvent into the cellulosic biomass solids.In some embodiments, washing or chemical treatment of the cellulosicbiomass solids may occur within the hydrothermal digestion unit beforehydrothermal digestion occurs. In other embodiments, washing or chemicaltreatment of the cellulosic biomass solids may occur before the biomassis provided in the hydrothermal digestion unit.

In some embodiments, the present methods may further comprise performinga phase separation of the reaction product. In various embodiments,performing a phase separation may comprise separating a bilayer,conducting a solvent stripping operation, performing an extraction,performing a filtration, performing a distillation, or the like. In someembodiments, azeotropic distillation may be conducted.

In some embodiments, the methods described herein may further compriseconverting the reaction product into a biofuel. As used herein, the term“biofuel” will refer to any transportation fuel formed from a biologicalsource. Such biofuels may also be referred to herein as “fuel blends.”In some embodiments, conversion of the reaction product into a biofuelmay begin with a catalytic reduction reaction to transform solublecarbohydrates produced from hydrothermal digestion into a more stablereaction product, as described above. In some embodiments, the reactionproduct may be further transformed by any number of further catalyticreforming reactions including, for example, further catalytic reductionreactions (e.g., hydrogenolysis reactions, hydrogenation reactions,hydrotreating reactions, and the like), condensation reactions,isomerization reactions, desulfurization reactions, dehydrationreactions, oligomerization reactions, alkylation reactions, and thelike. A description of the initial hydrogenolysis reaction and thefurther catalytic reforming reactions are described hereinafter.

Various processes are known for performing hydrogenolysis ofcarbohydrates. One suitable method includes contacting a carbohydrate orstable hydroxyl intermediate with hydrogen, optionally mixed with adiluent gas, and a hydrogenolysis catalyst under conditions effective toform a reaction product comprising oxygenated intermediates such as, forexample, smaller molecules or polyols. As used herein, the term “smallermolecules or polyols” includes any molecule that have a lower molecularweight, which may include a smaller number of carbon atoms or oxygenatoms, than the starting carbohydrate. In some embodiments, the reactionproducts may include smaller molecules such as, for example, polyols andalcohols. This aspect of hydrogenolysis entails the breaking ofcarbon-carbon bonds.

In some embodiments, a soluble carbohydrate may be converted torelatively stable oxygenated intermediates such as, for example,propylene glycol, ethylene glycol, and glycerol using a hydrogenolysisreaction in the presence of a catalyst that is capable of activatingmolecular hydrogen. Suitable catalysts may include, for example, Cr, Mo,W, Re, Mn, Cu, Cd, Fe, Co, Ni, Pt, Pd, Rh, Ru, Ir, Os, and alloys or anycombination thereof, either alone or with promoters such as Au, Ag, Cr,Zn, Mn, Sn, Bi, B, O, and alloys or any combination thereof. In someembodiments, the catalysts and promoters may allow for hydrogenation andhydrogenolysis reactions to occur at the same time or in succession,such as the hydrogenation of a carbonyl group to form an alcohol. Thecatalyst may also include a carbonaceous pyropolymer catalyst containingtransition metals (e.g., chromium, molybdenum, tungsten, rhenium,manganese, copper, and cadmium) or Group VIII metals (e.g., iron,cobalt, nickel, platinum, palladium, rhodium, ruthenium, iridium, andosmium). In certain embodiments, the catalyst may include any of theabove metals combined with an alkaline earth metal oxide or adhered to acatalytically active support. In certain embodiments, the catalystdescribed in the hydrogenolysis reaction may include a catalyst support.

The conditions under which to carry out the hydrogenolysis reaction willvary based on the type of biomass starting material and the desiredproducts (e.g. gasoline or diesel), for example. One of ordinary skillin the art, with the benefit of this disclosure, will recognize theappropriate conditions to use to carry out the reaction. In general, thehydrogenolysis reaction may be conducted at temperatures in the range ofabout 110° C. to about 300° C., and preferably from about 170° C. toabout 300° C., and most preferably from about 180° C. to about 290° C.

In some embodiments, the hydrogenolysis reaction may be conducted underbasic conditions, preferably at a pH of about 8 to about 13, and evenmore preferably at a pH of about 10 to about 12. In some embodiments,the hydrogenolysis reaction may be conducted at a pressure rangingbetween about 1 bar (absolute) and about 150 bar, and preferably at apressure ranging between about 15 bar and about 140 bar, and even morepreferably at a pressure ranging between 50 bar and 110 bar.

The hydrogen used in the hydrogenolysis reaction may include externalhydrogen, recycled hydrogen, in situ generated hydrogen, or anycombination thereof.

In some embodiments, the reaction products of the hydrogenolysisreaction may comprise greater than about 25% by mole, or alternatively,greater than about 30% by mole of polyols, which may result in a greaterconversion to a biofuel in a subsequent processing reaction.

In some embodiments, hydrogenolysis may be conducted under neutral oracidic conditions, as needed to accelerate hydrolysis reactions inaddition to the hydrogenolysis reaction. For example, hydrolysis ofoligomeric carbohydrates may be combined with hydrogenation to producesugar alcohols, which may undergo hydrogenolysis.

A second aspect of hydrogenolysis entails the breaking of —OH bonds suchas: RC(H)₂—OH+H₂→RCH₃+H₂O. This reaction is also called“hydrodeoxygenation,” and may occur in parallel with C—C bond breakinghydrogenolysis. Diols may be converted to mono-oxygenates via thisreaction. As reaction severity is increased with increased temperatureor contact time with catalyst, the concentration of polyols and diolsrelative to mono-oxygenates may diminish as a result ofhydrodeoxygenation. Selectivity for C—C vs. C—OH bond hydrogenolysiswill vary with catalyst type and formulation. Full de-oxygenation toalkanes may also occur, but is generally undesirable if the intent is toproduce mono-oxygenates or diols and polyols which may be condensed oroligomerized to higher molecular weight compounds in a subsequentprocessing step. Typically, it is desirable to send only mono-oxygenatesor diols to subsequent processing steps, as higher polyols may lead toexcessive coke formation during condensation or oligomerization.Alkanes, in contrast, are essentially unreactive and cannot be readilycombined to produce higher molecular compounds.

Once oxygenated intermediates have been formed by a hydrogenolysisreaction, a portion of the reaction product may be recirculated to thehydrothermal digestion unit to serve as an internally generateddigestion solvent. Another portion of the reaction product may bewithdrawn and subsequently processed by further reforming reactions toform a biofuel. Before being subjected to the further reformingreactions, the oxygenated intermediates may optionally be separated intodifferent components. Suitable separations may include, for example,phase separation, solvent stripping columns, extractors, filters,distillations and the like. In some embodiments, a separation of ligninfrom the oxygenated intermediates may be conducted before the reactionproduct is subsequently processed further or recirculated to thehydrothermal digestion unit.

The oxygenated intermediates may be processed to produce a fuel blend inone or more processing reactions. In some embodiments, a condensationreaction may be used along with other reactions to generate a fuel blendand may be catalyzed by a catalyst comprising an acid, a base, or both.In general, without being limited to any particular theory, it isbelieved that the basic condensation reactions may involve a series ofsteps involving: (1) an optional dehydrogenation reaction; (2) anoptional dehydration reaction that may be acid catalyzed; (3) an aldolcondensation reaction; (4) an optional ketonization reaction; (5) anoptional furanic ring opening reaction; (6) hydrogenation of theresulting condensation products to form a >C4 hydrocarbon; and (7) anycombination thereof. Acid catalyzed condensations may similarly entailoptional hydrogenation or dehydrogenation reactions, dehydration, andoligomerization reactions. Additional polishing reactions may also beused to conform the product to a specific fuel standard, includingreactions conducted in the presence of hydrogen and a hydrogenationcatalyst to remove functional groups from final fuel product. In someembodiments, a basic catalyst, a catalyst having both an acid and a basefunctional site, and optionally comprising a metal function, may also beused to effect the condensation reaction.

In some embodiments, an aldol condensation reaction may be used toproduce a fuel blend meeting the requirements for a diesel fuel or jetfuel. Traditional diesel fuels are petroleum distillates rich inparaffinic hydrocarbons. They have boiling ranges as broad as 187° C. to417° C., which are suitable for combustion in a compression ignitionengine, such as a diesel engine vehicle. The American Society of Testingand Materials (ASTM) establishes the grade of diesel according to theboiling range, along with allowable ranges of other fuel properties,such as cetane number, cloud point, flash point, viscosity, anilinepoint, sulfur content, water content, ash content, copper stripcorrosion, and carbon residue. Thus, any fuel blend meeting ASTM D975may be defined as diesel fuel.

The present disclosure also provides methods to produce jet fuel. Jetfuel is clear to straw colored. The most common fuel is anunleaded/paraffin oil-based fuel classified as Aeroplane A-1, which isproduced to an internationally standardized set of specifications. Jetfuel is a mixture of a large number of different hydrocarbons, possiblyas many as a thousand or more. The range of their sizes (molecularweights or carbon numbers) is restricted by the requirements for theproduct, for example, freezing point or smoke point. Kerosene-typeAirplane fuel (including Jet A and Jet A-1) has a carbon numberdistribution between about C8 and C16. Wide-cut or naphtha-type Airplanefuel (including Jet B) typically has a carbon number distributionbetween about C5 and C15. A fuel blend meeting ASTM D1655 may be definedas jet fuel.

In certain embodiments, both Airplanes (Jet A and Jet B) contain anumber of additives. Useful additives include, but are not limited to,antioxidants, antistatic agents, corrosion inhibitors, and fuel systemicing inhibitor (FSII) agents. Antioxidants prevent gumming and usually,are based on alkylated phenols, for example, AO-30, AO-31, or AO-37.Antistatic agents dissipate static electricity and prevent sparking.Stadis 450 with dinonylnaphthylsulfonic acid (DINNSA) as the activeingredient, is an example. Corrosion inhibitors (e.g., DCI-4A) are usedfor civilian and military fuels, and DCI-6A is used for military fuels.FSII agents, include, for example, Di-EGME.

In some embodiments, the oxygenated intermediates may comprise acarbonyl-containing compound that may take part in a base catalyzedcondensation reaction. In some embodiments, an optional dehydrogenationreaction may be used to increase the amount of carbonyl-containingcompounds in the oxygenated intermediate stream to be used as a feed tothe condensation reaction. In these embodiments, the oxygenatedintermediates and/or a portion of the bio-based feedstock stream may bedehydrogenated in the presence of a catalyst.

In some embodiments, a dehydrogenation catalyst may be preferred for anoxygenated intermediate stream comprising alcohols, diols, and triols.In general, alcohols cannot participate in aldol condensation directly.The hydroxyl group or groups present may be converted into carbonyls(e.g., aldehydes, ketones, etc.) in order to participate in an aldolcondensation reaction. A dehydrogenation catalyst may be included toeffect dehydrogenation of any alcohols, diols, or polyols present toform ketones and aldehydes. The dehydration catalyst is typically formedfrom the same metals as used for hydrogenation, hydrogenolysis, oraqueous phase reforming. These catalysts are described in more detailabove. Dehydrogenation yields may be enhanced by the removal orconsumption of hydrogen as it forms during the reaction. Thedehydrogenation step may be carried out as a separate reaction stepbefore an aldol condensation reaction, or the dehydrogenation reactionmay be carried out in concert with the aldol condensation reaction. Forconcerted dehydrogenation and aldol condensation reactions, thedehydrogenation and aldol condensation functions may take place on thesame catalyst. For example, a metal hydrogenation/dehydrogenationfunctionality may be present on catalyst comprising a basicfunctionality.

The dehydrogenation reaction may result in the production of acarbonyl-containing compound. Suitable carbonyl-containing compounds mayinclude, but are not limited to, any compound comprising a carbonylfunctional group that may form carbanion species or may react in acondensation reaction with a carbanion species. In an embodiment, acarbonyl-containing compound may include, but is not limited to,ketones, aldehydes, furfurals, hydroxy carboxylic acids, and, carboxylicacids. Ketones may include, without limitation, hydroxyketones, cyclicketones, diketones, acetone, propanone, 2-oxopropanal, butanone,butane-2,3-dione, 3-hydroxybutane-2-one, pentanone, cyclopentanone,pentane-2,3-dione, pentane-2,4-dione, hexanone, cyclohexanone,2-methyl-cyclopentanone, heptanone, octanone, nonanone, decanone,undecanone, dodecanone, methylglyoxal, butanedione, pentanedione,diketohexane, dihydroxyacetone, and isomers thereof. Aldehydes mayinclude, without limitation, hydroxyaldehydes, acetaldehyde,glyceraldehyde, propionaldehyde, butyraldehyde, pentanal, hexanal,heptanal, octanal, nonal, decanal, undecanal, dodecanal, and isomersthereof. Carboxylic acids may include, without limitation, formic acid,acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoicacid, heptanoic acid, isomers and derivatives thereof, includinghydroxylated derivatives, such as 2-hydroxybutanoic acid and lacticacid. Furfurals may include, without limitation, hydroxylmethylfurfural,5-hydroxymethyl-2(5H)-furanone,dihydro-5-(hydroxymethyl)-2(3H)-furanone, tetrahydro-2-furoic acid,dihydro-5-(hydroxymethyl)-2(3H)-furanone, tetrahydrofurfuryl alcohol,1-(2-furyl)ethanol, hydroxymethyltetrahydrofurfural, and isomersthereof. In an embodiment, the dehydrogenation reaction may result inthe production of a carbonyl-containing compound that is combined withthe oxygenated intermediates to become a part of the oxygenatedintermediates fed to the condensation reaction.

In an embodiment, an acid catalyst may be used to optionally dehydrateat least a portion of the oxygenated intermediate stream. Suitable acidcatalysts for use in the dehydration reaction may include, but are notlimited to, mineral acids (e.g., HCl, H₂SO₄), solid acids (e.g.,zeolites, ion-exchange resins) and acid salts (e.g., LaCl₃). Additionalacid catalysts may include, without limitation, zeolites, carbides,nitrides, zirconia, alumina, silica, aluminosilicates, phosphates,titanium oxides, zinc oxides, vanadium oxides, lanthanum oxides, yttriumoxides, scandium oxides, magnesium oxides, cerium oxides, barium oxides,calcium oxides, hydroxides, heteropolyacids, inorganic acids, acidmodified resins, base modified resins, and any combination thereof. Insome embodiments, the dehydration catalyst may also include a modifier.Suitable modifiers may include, for example, La, Y, Sc, P, B, Bi, Li,Na, K, Rb, Cs, Mg, Ca, Sr, Ba, and any combination thereof. Themodifiers may be useful, inter alia, to carry out a concertedhydrogenation/dehydrogenation reaction with the dehydration reaction. Insome embodiments, the dehydration catalyst may also include a metal.Suitable metals may include, for example, Cu, Ag, Au, Pt, Ni, Fe, Co,Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, alloys, andany combination thereof. The dehydration catalyst may be selfsupporting, supported on an inert support or resin, or it may bedissolved in solution.

In some embodiments, the dehydration reaction may occur in the vaporphase. In other embodiments, the dehydration reaction may occur in theliquid phase. For liquid phase dehydration reactions, an aqueoussolution may be used to carry out the reaction. In an embodiment, othersolvents in addition to water, may be used to form the aqueous solution.For example, water soluble organic solvents may be present. Suitablesolvents may include, but are not limited to, hydroxymethylfurfural(HMF), dimethylsulfoxide (DMSO), 1-methyl-n-pyrollidone (NMP), and anycombination thereof. Other suitable aprotic solvents may also be usedalone or in combination with any of these solvents.

In an embodiment, the processing reactions may comprise an optionalketonization reaction. A ketonization reaction may increase the numberof ketone functional groups within at least a portion of the oxygenatedintermediates. For example, an alcohol may be converted into a ketone ina ketonization reaction. Ketonization may be carried out in the presenceof a basic catalyst. Any of the basic catalysts described above as thebasic component of the aldol condensation reaction may be used to effecta ketonization reaction. Suitable reaction conditions are known to oneof ordinary skill in the art and generally correspond to the reactionconditions listed above with respect to the aldol condensation reaction.The ketonization reaction may be carried out as a separate reactionstep, or it may be carried out in concert with the aldol condensationreaction. The inclusion of a basic functional site on the aldolcondensation catalyst may result in concerted ketonization and aldolcondensation reactions.

In some embodiments, the processing reactions may comprise an optionalfuranic ring opening reaction. A furanic ring opening reaction mayresult in the conversion of at least a portion of any oxygenatedintermediates comprising a furanic ring into compounds that are morereactive in an aldol condensation reaction. A furanic ring openingreaction may be carried out in the presence of an acidic catalyst. Anyof the acid catalysts described above as the acid component of the aldolcondensation reaction may be used to effect a furanic ring openingreaction. Suitable reaction conditions are known to one of ordinaryskill in the art and generally correspond to the reaction conditionslisted above with respect to the aldol condensation reaction. Thefuranic ring opening reaction may be carried out as a separate reactionstep, or it may be carried out in concert with the aldol condensationreaction. The inclusion of an acid functional site on the aldolcondensation catalyst may result in a concerted furanic ring openingreaction and aldol condensation reactions. Such an embodiment may beadvantageous as any furanic rings may be opened in the presence of anacid functionality and reacted in an aldol condensation reaction using abasic functionality. Such a concerted reaction scheme may allow for theproduction of a greater amount of higher hydrocarbons to be formed for agiven oxygenated intermediate feed.

In some embodiments, production of a >C4 compound may occur bycondensation, which may include aldol condensation of the oxygenatedintermediates in the presence of a condensation catalyst.Aldol-condensation generally involves the carbon-carbon coupling betweentwo compounds, at least one of which may contain a carbonyl group, toform a larger organic molecule. For example, acetone may react withhydroxymethylfurfural to form a C9 species, which may subsequently reactwith another hydroxymethylfurfural molecule to form a C15 species. Invarious embodiments, the reaction is usually carried out in the presenceof a condensation catalyst. The condensation reaction may be carried outin the vapor or liquid phase. In an embodiment, the reaction may takeplace at a temperature ranging from about 5° C. to about 375° C.depending on the reactivity of the carbonyl group.

The condensation catalyst will generally be a catalyst capable offorming longer chain compounds by linking two molecules through a newcarbon-carbon bond, such as a basic catalyst, a mufti-functionalcatalyst having both acid and base functionalities, or either type ofcatalyst also comprising an optional metal functionality. In someembodiments, the mufti-functional catalyst may be a catalyst having bothstrong acid and strong base functionalities. In some embodiments, aldolcatalysts may comprise Li, Na, K, Cs, B, Rb, Mg, Ca, Sr, Si, Ba, Al, Zn,Ce, La, Y, Sc, Y, Zr, Ti, hydrotalcite, zinc-aluminate, phosphate,base-treated aluminosilicate zeolite, a basic resin, basic nitride,alloys or any combination thereof. In some embodiments, the basecatalyst may also comprise an oxide of Ti, Zr, V, Nb, Ta, Mo, Cr, W, Mn,Re, Al, Ga, In, Co, Ni, Si, Cu, Zn, Sn, Cd, Mg, P, Fe, or anycombination thereof. In some embodiments, the condensation catalystcomprises mixed-oxide base catalysts. Suitable mixed-oxide basecatalysts may comprise a combination of magnesium, zirconium, andoxygen, which may comprise, without limitation: Si—Mg—O, Mg—Ti—O,Y—Mg—O, Y—Zr—O, Ti—Zr—O, Ce—Zr—O, Ce—Mg—O, Ca—Zr—O, La—Zr—O, B—Zr—O,La—Ti—O, B—Ti—O, and any combination thereof. Different atomic ratios ofMg/Zr or the combinations of various other elements constituting themixed oxide catalyst may be used ranging from about 0.01 to about 50. Insome embodiments, the condensation catalyst may further include a metalor alloys comprising metals, such as Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn,Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Bi, Pb, Os, alloys andcombinations thereof. Such metals may be preferred when adehydrogenation reaction is to be carried out in concert with the aldolcondensation reaction. In some embodiments, preferred Group IA materialsmay include Li, Na, K, Cs and Rb. In some embodiments, preferred GroupIIA materials may include Mg, Ca, Sr and Ba. In some embodiments, GroupIIB materials may include Zn and Cd. In some embodiments, Group IIIBmaterials may include Y and La. Basic resins may include resins thatexhibit basic functionality. The basic catalyst may be self-supportingor adhered to any one of the supports further described below, includingsupports containing carbon, silica, alumina, zirconia, titania, vanadia,ceria, nitride, boron nitride, heteropolyacids, alloys and mixturesthereof.

In one embodiment, the condensation catalyst may be derived from thecombination of MgO and Al₂O₃ to form a hydrotalcite material. Anotherpreferred material contains ZnO and Al₂O₃ in the form of a zincaluminate spinel. Yet another preferred material is a combination ofZnO, Al₂O₃, and CuO. Each of these materials may also contain anadditional metal function provided by a Group VIIIB metal, such as Pd orPt. Such metals may be preferred when a dehydrogenation reaction is tobe carried out in concert with the aldol condensation reaction. In someembodiments, the basic catalyst may be a metal oxide containing Cu, Ni,Zn, V, Zr, or mixtures thereof. In other embodiments, the basic catalystmay be a zinc aluminate metal containing Pt, Pd Cu, Ni, or mixturesthereof.

In some embodiments, a base-catalyzed condensation reaction may beperformed using a condensation catalyst with both an acidic and a basicfunctionality. The acid-aldol condensation catalyst may comprisehydrotalcite, zinc-aluminate, phosphate, Li, Na, K, Cs, B, Rb, Mg, Si,Ca, Sr, Ba, Al, Ce, La, Sc, Y, Zr, Ti, Zn, Cr, or any combinationthereof. In further embodiments, the acid-base catalyst may also includeone or more oxides from the group of Ti, Zr, V, Nb, Ta, Mo, Cr, W, Mn,Re, Al, Ga, In, Fe, Co, Ir, Ni, Si, Cu, Zn, Sn, Cd, P, and combinationsthereof. In some embodiments, the acid-base catalyst may include a metalfunctionality provided by Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga,In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, alloys or combinationsthereof. In some embodiments, the catalyst may further include Zn, Cd orphosphate. In some embodiments, the condensation catalyst may be a metaloxide containing Pd, Pt, Cu or Ni, and even more preferably an aluminateor zirconium metal oxide containing Mg and Cu, Pt, Pd or Ni. Theacid-base catalyst may also include a hydroxyapatite (HAP) combined withany one or more of the above metals. The acid-base catalyst may beself-supporting or adhered to any one of the supports further describedbelow, including supports containing carbon, silica, alumina, zirconia,titania, vanadia, ceria, nitride, boron nitride, heteropolyacids, alloysand mixtures thereof.

In some embodiments, the condensation catalyst may also include zeolitesand other microporous supports that contain Group IA compounds, such asLi, Na, K, Cs and Rb. Preferably, the Group IA material may be presentin an amount less than that required to neutralize the acidic nature ofthe support. A metal function may also be provided by the addition ofgroup VIIIB metals, or Cu, Ga, In, Zn or Sn. In one embodiment, thecondensation catalyst may be derived from the combination of MgO andAl₂O₃ to form a hydrotalcite material. Another preferred material maycontain a combination of MgO and ZrO₂, or a combination of ZnO andAl₂O₃. Each of these materials may also contain an additional metalfunction provided by copper or a Group VIIIB metal, such as Ni, Pd, Pt,or combinations of the foregoing.

The condensation catalyst may be self-supporting (i.e., the catalystdoes not need another material to serve as a support), or may require aseparate support suitable for suspending the catalyst in the reactantstream. One exemplary support is silica, especially silica having a highsurface area (greater than 100 square meters per gram), obtained bysol-gel synthesis, precipitation, or fuming. In other embodiments,particularly when the condensation catalyst is a powder, the catalystsystem may include a binder to assist in forming the catalyst into adesirable catalyst shape. Applicable forming processes may includeextrusion, pelletization, oil dropping, or other known processes. Zincoxide, alumina, and a peptizing agent may also be mixed together andextruded to produce a formed material. After drying, this material maybe calcined at a temperature appropriate for formation of thecatalytically active phase. Other catalyst supports as known to onehaving ordinary skill in the art may also be used.

In some embodiments, a dehydration catalyst, a dehydrogenation catalyst,and the condensation catalyst may be present in the same reactor as thereaction conditions overlap to some degree. In these embodiments, adehydration reaction and/or a dehydrogenation reaction may occursubstantially simultaneously with the condensation reaction. In someembodiments, a catalyst may comprise active sites for a dehydrationreaction and/or a dehydrogenation reaction in addition to a condensationreaction. For example, a catalyst may comprise active metals for adehydration reaction and/or a dehydrogenation reaction along with acondensation reaction at separate sites on the catalyst or as alloys.Suitable active elements may comprise any of those listed above withrespect to the dehydration catalyst, dehydrogenation catalyst, and thecondensation catalyst. Alternately, a physical mixture of dehydration,dehydrogenation, and condensation catalysts may be employed. While notintending to be limited by theory, it is believed that using acondensation catalyst comprising a metal and/or an acid functionalitymay assist in pushing the equilibrium limited aldol condensationreaction toward completion. Advantageously, this may be used to effectmultiple condensation reactions with dehydration and/or dehydrogenationof intermediates, in order to form (via condensation, dehydration,and/or dehydrogenation) higher molecular weight oligomers as desired toproduce jet or diesel fuel.

The specific >C4 compounds produced in the condensation reaction maydepend on various factors, including, without limitation, the type ofoxygenated intermediates in the reactant stream, condensationtemperature, condensation pressure, the reactivity of the catalyst, andthe flow rate of the reactant stream. In general, the condensationreaction may be carried out at a temperature at which the thermodynamicsof the proposed reaction are favorable. For condensed phase liquidreactions, the pressure within the reactor may be sufficient to maintainat least a portion of the reactants in the condensed liquid phase at thereactor inlet. For vapor phase reactions, the reaction may be carriedout at a temperature where the vapor pressure of the oxygenates is atleast about 0.1 bar, and the thermodynamics of the reaction arefavorable. The condensation temperature will vary depending upon thespecific oxygenated intermediates used, but may generally range betweenabout 75° C. and about 500° C. for reactions taking place in the vaporphase, and more preferably range between about 125° C. and about 450° C.For liquid phase reactions, the condensation temperature may rangebetween about 5° C. and about 475° C., and the condensation pressure mayrange between about 0.01 bar and about 100 bar. Preferably, thecondensation temperature may range between about 15° C. and about 300°C., or between about 15° C. and 250° C.

Varying the factors above, as well as others, will generally result in amodification to the specific composition and yields of the >C4compounds. For example, varying the temperature and/or pressure of thereactor system, or the particular catalyst formulations, may result inthe production of >C4 alcohols and/or ketones instead of >C4hydrocarbons. The >C4 hydrocarbon product may also contain a variety ofolefins, and alkanes of various sizes (typically branched alkanes).Depending upon the condensation catalyst used, the hydrocarbon productmay also include aromatic and cyclic hydrocarbon compounds. The >C4hydrocarbon product may also contain undesirably high levels of olefins,which may lead to coking or deposits in combustion engines, or otherundesirable hydrocarbon products. In such cases, the hydrocarbons mayoptionally be hydrogenated to reduce the ketones to alcohols andhydrocarbons, while the alcohols and olefinic hydrocarbons may bereduced to alkanes, thereby forming a more desirable hydrocarbon producthaving reduced levels of olefins, aromatics or alcohols.

The condensation reactions may be carried out in any reactor of suitabledesign, including continuous-flow, batch, semi-batch or multi-systemreactors, without limitation as to design, size, geometry, flow rates,and the like. The reactor system may also use a fluidized catalytic bedsystem, a swing bed system, fixed bed system, a moving bed system, or acombination of the above. In some embodiments, bi-phasic (e.g.,liquid-liquid) and tri-phasic (e.g., liquid-liquid-solid) reactors maybe used to carry out the condensation reactions.

In a continuous flow system, the reactor system may include an optionaldehydrogenation bed adapted to produce dehydrogenated oxygenatedintermediates, an optional dehydration bed adapted to produce dehydratedoxygenated intermediates, and a condensation bed adapted to produce >C4compounds from the oxygenated intermediates. The dehydrogenation bed maybe configured to receive the reactant stream and produce the desiredoxygenated intermediates, which may have an increase in the amount ofcarbonyl-containing compounds. The dehydration bed may be configured toreceive the reactant stream and produce the desired oxygenatedintermediates. The condensation bed may be configured to receive theoxygenated intermediates for contact with the condensation catalyst andproduction of the desired >C4 compounds. For systems with one or morefinishing steps, an additional reaction bed for conducting the finishingprocess or processes may be included after the condensation bed.

In some embodiments, the optional dehydration reaction, the optionaldehydrogenation reaction, the optional ketonization reaction, theoptional ring opening reaction, and the condensation reaction catalystbeds may be positioned within the same reactor vessel or in separatereactor vessels in fluid communication with each other. Each reactorvessel preferably may include an outlet adapted to remove the productstream from the reactor vessel. For systems with one or more finishingsteps, the finishing reaction bed or beds may be within the same reactorvessel along with the condensation bed or in a separate reactor vesselin fluid communication with the reactor vessel having the condensationbed.

In some embodiments, the reactor system also may include additionaloutlets to allow for the removal of portions of the reactant stream tofurther advance or direct the reaction to the desired reaction products,and to allow for the collection and recycling of reaction byproducts foruse in other portions of the system. In some embodiments, the reactorsystem also may include additional inlets to allow for the introductionof supplemental materials to further advance or direct the reaction tothe desired reaction products, and to allow for the recycling ofreaction byproducts for use in other reactions.

In some embodiments, the reactor system also may include elements whichallow for the separation of the reactant stream into differentcomponents which may find use in different reaction schemes or to simplypromote the desired reactions. For instance, a separator unit, such as aphase separator, extractor, purifier or distillation column, may beinstalled prior to the condensation step to remove water from thereactant stream for purposes of advancing the condensation reaction tofavor the production of higher hydrocarbons. In some embodiments, aseparation unit may be installed to remove specific intermediates toallow for the production of a desired product stream containinghydrocarbons within a particular carbon number range, or for use as endproducts or in other systems or processes. The condensation reaction mayproduce a broad range of compounds with carbon numbers ranging from C4to C30 or greater. Exemplary compounds may include, for example, >C4alkanes, >C4 alkenes, >C5 cycloalkanes, >C5 cycloalkenes, aryls, fusedaryls, >C4 alcohols, >C4 ketones, and mixtures thereof. The >C4 alkanesand >C4 alkenes may range from 4 to about 30 carbon atoms (i.e. C4-C30alkanes and C4-C30 alkenes) and may be branched or straight chainalkanes or alkenes. The >C4 alkanes and >C4 alkenes may also includefractions of C7-C14, C12-C24 alkanes and alkenes, respectively, with theC7-C14 fraction directed to jet fuel blends, and the C12-C24 fractiondirected to diesel fuel blends and other industrial applications.Examples of various >C4 alkanes and >C4 alkenes may include, withoutlimitation, butane, butene, pentane, pentene, 2-methylbutane, hexane,hexene, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane,2,3-dimethylbutane, heptane, heptene, octane, octene,2,2,4-trimethylpentane, 2,3-dimethyl hexane, 2,3,4-trimethylpentane,2,3-dimethylpentane, nonane, nonene, decane, decene, undecane, undecene,dodecane, dodecene, tridecane, tridecene, tetradecane, tetradecene,pentadecane, pentadecene, hexadecane, hexadecene, heptyldecane,heptyldecene, octyldecane, octyldecene, nonyldecane, nonyldecene,eicosane, eicosene, uneicosane, uneicosene, doeicosane, doeicosene,trieicosane, trieicosene, tetraeicosane, tetraeicosene, and isomersthereof.

The >C5 cycloalkanes and >C5 cycloalkenes may have from 5 to about 30carbon atoms and may be unsubstituted, mono-substituted ormufti-substituted. In the case of mono-substituted and mufti-substitutedcompounds, the substituted group may include a branched >C3 alkyl, astraight chain >C1 alkyl, a branched >C3 alkylene, a straight chain >C1alkylene, a straight chain >C2 alkylene, an aryl group, or a combinationthereof. In one embodiment, at least one of the substituted groups mayinclude a branched C3-C12 alkyl, a straight chain C1-C12 alkyl, abranched C3-C12 alkylene, a straight chain C1-C12 alkylene, a straightchain C2-C12 alkylene, an aryl group, or a combination thereof. In yetother embodiments, at least one of the substituted groups may include abranched C3-C4 alkyl, a straight chain C1-C4 alkyl, a branched C3-C4alkylene, a straight chain C1-C4 alkylene, a straight chain C2-C4alkylene, an aryl group, or any combination thereof. Examples ofdesirable >C5 cycloalkanes and >C5 cycloalkenes may include, withoutlimitation, cyclopentane, cyclopentene, cyclohexane, cyclohexene,methylcyclopentane, methylcyclopentene, ethylcyclopentane,ethylcyclopentene, ethylcyclohexane, ethylcyclohexene, and isomersthereof.

Aryl groups contain an aromatic hydrocarbon in either an unsubstituted(phenyl), mono-substituted or mufti-substituted form. In the case ofmono-substituted and multi-substituted compounds, the substituted groupmay include a branched >C3 alkyl, a straight chain >C1 alkyl, abranched >C3 alkylene, a straight chain >C2 alkylene, a phenyl group, ora combination thereof. In some embodiments, at least one of thesubstituted groups may include a branched C3-C12 alkyl, a straight chainC1-C12 alkyl, a branched C3-C12 alkylene, a straight chain C2-C12alkylene, a phenyl group, or any combination thereof. In yet otherembodiments, at least one of the substituted groups may include abranched C3-C4 alkyl, a straight chain C1-C4 alkyl, a branched C3-C4alkylene, a straight chain C2-C4 alkylene, a phenyl group, or anycombination thereof. Examples of various aryl compounds may include,without limitation, benzene, toluene, xylene (dimethylbenzene), ethylbenzene, para-xylene, meta-xylene, ortho-xylene, and C9 aromatics.

Fused aryls contain bicyclic and polycyclic aromatic hydrocarbons, ineither an unsubstituted, mono-substituted or multi-substituted form. Inthe case of mono-substituted and mufti-substituted compounds, thesubstituted group may include a branched >C3 alkyl, a straight chain >C1alkyl, a branched >C3 alkylene, a straight chain >C2 alkylene, a phenylgroup, or a combination thereof. In other embodiments, at least one ofthe substituted groups may include a branched C3-C4 alkyl, a straightchain C1-C4 alkyl, a branched C3-C4 alkylene, a straight chain C2-C4alkylene, a phenyl group, or any combination thereof. Examples ofvarious fused aryls may include, without limitation, naphthalene,anthracene, tetrahydronaphthalene, and decahydronaphthalene, indane,indene, and isomers thereof.

The moderate fractions, such as C7-C14, may be separated for jet fuel,while heavier fractions, such as C12-C24, may be separated for dieseluse. The heaviest fractions may be used as lubricants or cracked toproduce additional gasoline and/or diesel fractions. The >C4 compoundsmay also find use as industrial chemicals, whether as an intermediate oran end product. For example, the aryls toluene, xylene, ethylbenzene,para-xylene, meta-xylene, and ortho-xylene may find use as chemicalintermediates for the production of plastics and other products.Meanwhile, C9 aromatics and fused aryls, such as naphthalene,anthracene, tetrahydronaphthalene, and decahydronaphthalene, may finduse as solvents in industrial processes.

In some embodiments, additional processes may be used to treat the fuelblend to remove certain components or further conform the fuel blend toa diesel or jet fuel standard. Suitable techniques may includehydrotreating to reduce the amount of or remove any remaining oxygen,sulfur, or nitrogen in the fuel blend. The conditions for hydrotreatinga hydrocarbon stream will be known to one of ordinary skill in the art.

In some embodiments, hydrogenation may be carried out in place of orafter the hydrotreating process to saturate at least some olefinicbonds. In some embodiments, a hydrogenation reaction may be carried outin concert with the aldol condensation reaction by including a metalfunctional group with the aldol condensation catalyst. Suchhydrogenation may be performed to conform the fuel blend to a specificfuel standard (e.g., a diesel fuel standard or a jet fuel standard). Thehydrogenation of the fuel blend stream may be carried out according toknown procedures, either with the continuous or batch method. Thehydrogenation reaction may be used to remove remaining carbonyl groupsand/or hydroxyl groups. In such cases, any of the hydrogenationcatalysts described above may be used. In general, the finishing stepmay be carried out at finishing temperatures ranging between about 80°C. and about 250° C., and finishing pressures may range between about 5bar and about 150 bar. In some embodiments, the finishing step may beconducted in the vapor phase or liquid phase, and use, externalhydrogen, recycled hydrogen, or combinations thereof, as necessary.

In some embodiments, isomerization may be used to treat the fuel blendto introduce a desired degree of branching or other shape selectivity toat least some components in the fuel blend. It may also be useful toremove any impurities before the hydrocarbons are contacted with theisomerization catalyst. The isomerization step may comprise an optionalstripping step, wherein the fuel blend from the oligomerization reactionmay be purified by stripping with water vapor or a suitable gas such aslight hydrocarbon, nitrogen or hydrogen. The optional stripping step maybe carried out in a countercurrent manner in a unit upstream of theisomerization catalyst, wherein the gas and liquid are contacted witheach other, or before the actual isomerization reactor in a separatestripping unit utilizing countercurrent principle.

After the optional stripping step the fuel blend may be passed to areactive isomerization unit comprising one or more catalyst beds. Thecatalyst beds of the isomerization unit may operate either in co-currentor countercurrent manner. In the isomerization unit, the pressure mayvary between about 20 bar to about 150 bar, preferably between about 20bar to about 100 bar, the temperature ranging between about 195° C. andabout 500° C., preferably between about 300° C. and about 400° C.

In the isomerization unit, any isomerization catalyst known in the artmay be used. In some embodiments, suitable isomerization catalysts maycontain molecular sieve and/or a metal from Group VII and/or a carrier.In some embodiments, the isomerization catalyst may contain SAPO-11 orSAPO41 or ZSM-22 or ZSM-23 or ferrierite and Pt, Pd or Ni and Al₂O₃ orSiO₂. Typical isomerization catalysts may include, for example,Pt/SAPO-11/Al₂O₃, Pt/ZSM-22/Al₂O₃, Pt/ZSM-23/Al₂O₃ and Pt/SAPO-11/SiO₂.

Other factors, such as the concentration of water or undesiredoxygenated intermediates, may also effect the composition and yields ofthe >C4 compounds, as well as the activity and stability of thecondensation catalyst. In such cases, the process may include adewatering step that removes a portion of the water prior to thecondensation reaction and/or the optional dehydration reaction, or aseparation unit for removal of the undesired oxygenated intermediates.For instance, a separator unit, such as a phase separator, extractor,purifier or distillation column, may be installed prior to thecondensation reactor so as to remove a portion of the water from thereactant stream containing the oxygenated intermediates. A separationunit may also be installed to remove specific oxygenated intermediatesto allow for the production of a desired product stream containinghydrocarbons within a particular carbon range, or for use as endproducts or in other systems or processes.

Thus, in some embodiments, the fuel blend produced by the processesdescribed herein may be a hydrocarbon mixture that meets therequirements for jet fuel (e.g., conforms with ASTM D1655). In otherembodiments, the product of the processes described herein may be ahydrocarbon mixture that comprises a fuel blend meeting the requirementsfor a diesel fuel (e.g., conforms with ASTM D975).

In other embodiments, a fuel blend comprising gasoline hydrocarbons(i.e., a gasoline fuel) may be produced. “Gasoline hydrocarbons” referto hydrocarbons predominantly comprising C5-9 hydrocarbons, for example,C6-8 hydrocarbons, and having a boiling point range from 32° C. (90° F.)to about 204° C. (400° F.). Gasoline hydrocarbons may include, but arenot limited to, straight run gasoline, naphtha, fluidized or thermallycatalytically cracked gasoline, VB gasoline, and coker gasoline.Gasoline hydrocarbons content is determined by ASTM Method D2887.

In yet other embodiments, the >C2 olefins may be produced bycatalytically reacting the oxygenated intermediates in the presence of adehydration catalyst at a dehydration temperature and dehydrationpressure to produce a reaction stream comprising the >C2 olefins.The >C2 olefins may comprise straight or branched hydrocarbonscontaining one or more carbon-carbon double bonds. In general, the >C2olefins may contain from 2 to 8 carbon atoms, and more preferably from 3to 5 carbon atoms. In some embodiments, the olefins may comprisepropylene, butylene, pentylene, isomers of the foregoing, and mixturesof any two or more of the foregoing. In other embodiments, the >C2olefins may include >C4 olefins produced by catalytically reacting aportion of the >C2 olefins over an olefin isomerization catalyst.

The dehydration catalyst may comprise a member selected from the groupconsisting of an acidic alumina, aluminum phosphate, silica-aluminaphosphate, amorphous silica-alumina, aluminosilicate, zirconia, sulfatedzirconia, tungstated zirconia, tungsten carbide, molybdenum carbide,titania, sulfated carbon, phosphated carbon, phosphated silica,phosphated alumina, acidic resin, heteropolyacid, inorganic acid, and acombination of any two or more of the foregoing. In some embodiments,the dehydration catalyst may further comprise a modifier selected fromthe group consisting of Ce, Y, Sc, La, Li, Na, K, Rb, Cs, Mg, Ca, Sr,Ba, P, B, Bi, and a combination of any two or more of the foregoing. Inother embodiments, the dehydration catalyst may further comprise anoxide of an element, the element selected from the group consisting ofTi, Zr, V, Nb, Ta, Mo, Cr, W, Mn, Re, Al, Ga, In, Fe, Co, Ir, Ni, Si,Cu, Zn, Sn, Cd, P, and a combination of any two or more of theforegoing. In yet other embodiments, the dehydration catalyst mayfurther comprise a metal selected from the group consisting of Cu, Ag,Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W,Sn, Os, an alloy of any two or more of the foregoing, and a combinationof any two or more of the foregoing.

In yet other embodiments, the dehydration catalyst may comprise analuminosilicate zeolite. In some embodiments, the dehydration catalystmay further comprise a modifier selected from the group consisting ofGa, In, Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, a lanthanide, and acombination of any two or more of the foregoing. In some embodiments,the dehydration catalyst may further comprise a metal selected from thegroup consisting of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh,Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an alloy of any two or more of theforegoing, and a combination of any two or more of the foregoing.

In other embodiments, the dehydration catalyst may comprise abifunctional pentasil ring-containing aluminosilicate zeolite. In someembodiments, the dehydration catalyst may further comprise a modifierselected from the group consisting of Ga, In, Zn, Fe, Mo, Ag, Au, Ni, P,Sc, Y, Ta, a lanthanide, and a combination of any two or more of theforegoing. In some embodiments, the dehydration catalyst may furthercomprise a metal selected from the group consisting of Cu, Ag, Au, Pt,Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os,an alloy of any two or more of the foregoing, and a combination of anytwo or more of the foregoing.

The dehydration reaction may be conducted at a temperature and pressurewhere the thermodynamics are favorable. In general, the reaction may beperformed in the vapor phase, liquid phase, or a combination of both. Insome embodiments, the dehydration temperature may range between about100° C. and about 500° C., and the dehydration pressure may rangebetween about 1 bar (absolute) and about 60 bar. In some embodiments,the dehydration temperature may range between about 125° C. and about450° C. In some embodiments, the dehydration temperature may rangebetween about 150° C. and about 350° C., and the dehydration pressuremay range between about 5 bar and about 50 bar. In some embodiments, thedehydration temperature may range between about 175° C. and about 325°C.

The >C6 paraffins may be produced by catalytically reacting >C2 olefinswith a stream of >C4 isoparaffins in the presence of an alkylationcatalyst at an alkylation temperature and alkylation pressure to producea product stream comprising >C6 paraffins. The >C4 isoparaffins mayinclude alkanes and cycloalkanes having 4 to 7 carbon atoms, such asisobutane, isopentane, naphthenes, and higher homologues having atertiary carbon atom (e.g., 2-methylbutane and 2,4-dimethylpentane),isomers of the foregoing, and mixtures of any two or more of theforegoing. In some embodiments, the stream of >C4 isoparaffins maycomprise internally generated >C4 isoparaffins, external >C4isoparaffins, recycled >C4 isoparaffins, or combinations of any two ormore of the foregoing.

The >C6 paraffins may be branched paraffins, but may also include normalparaffins. In one version, the >C6 paraffins may comprise a memberselected from the group consisting of a branched C6-10 alkane, abranched C6 alkane, a branched C7 alkane, a branched C8 alkane, abranched C9 alkane, a branched C10 alkane, or a mixture of any two ormore of the foregoing. In one version, the >C6 paraffins may include,for example, dimethylbutane, 2,2-dimethylbutane, 2,3-dimethylbutane,methylpentane, 2-methylpentane, 3-methylpentane, dimethylpentane,2,3-dimethylpentane, 2,4-dimethylpentane, methylhexane,2,3-dimethylhexane, 2,3,4-trimethylpentane, 2,2,4-trimethylpentane,2,2,3-trimethylpentane, 2,3,3-trimethylpentane, dimethylhexane, ormixtures of any two or more of the foregoing.

The alkylation catalyst may comprise a member selected from the group ofsulfuric acid, hydrofluoric acid, aluminum chloride, boron trifluoride,solid phosphoric acid, chlorided alumina, acidic alumina, aluminumphosphate, silica-alumina phosphate, amorphous silica-alumina,aluminosilicate, aluminosilicate zeolite, zirconia, sulfated zirconia,tungstated zirconia, tungsten carbide, molybdenum carbide, titania,sulfated carbon, phosphated carbon, phosphated silica, phosphatedalumina, acidic resin, heteropolyacid, inorganic acid, and a combinationof any two or more of the foregoing. The alkylation catalyst may alsoinclude a mixture of a mineral acid with a Friedel-Crafts metal halide,such as aluminum bromide, and other proton donors.

In some embodiments, the alkylation catalyst may comprise analunninosilicate zeolite. In some embodiments, the alkylation catalystmay further comprise a modifier selected from the group consisting ofGa, In, Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, a lanthanide, and acombination of any two or more of the foregoing. In some embodiments,the alkylation catalyst may further comprise a metal selected from thegroup consisting of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh,Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an alloy of any two or more of theforegoing, and a combination of any two or more of the foregoing.

In some embodiments, the alkylation catalyst may comprise a bifunctionalpentasil ring-containing alunninosilicate zeolite. In some embodiments,the alkylation catalyst may further comprise a modifier selected fromthe group consisting of Ga, In, Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, alanthanide, and a combination of any two or more of the foregoing. Insome embodiments, the alkylation catalyst may further comprise a metalselected from the group consisting of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru,Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an alloy of anytwo or more of the foregoing, and a combination of any two or more ofthe foregoing. In one version, the dehydration catalyst and thealkylation catalyst may be atomically identical.

The alkylation reaction may be conducted at a temperature where thethermodynamics are favorable. In general, the alkylation temperature mayrange between about −20° C. and about 300° C., and the alkylationpressure may range between about 1 bar (absolute) and about 80 bar. Insome embodiments, the alkylation temperature may range between about100° C. and about 300° C. In another version, the alkylation temperaturemay range between about 0° C. and about 100° C. In yet otherembodiments, the alkylation temperature may range between about 0° C.and about 50° C. In still other embodiments, the alkylation temperaturemay range between about 70° C. and about 250° C., and the alkylationpressure may range between about 5 bar and about 80 bar. In someembodiments, the alkylation catalyst may comprise a mineral acid or astrong acid. In other embodiments, the alkylation catalyst may comprisea zeolite and the alkylation temperature may be greater than about 100°C.

In some embodiments, an olefinic oligomerization reaction may beconducted. The oligomerization reaction may be carried out in anysuitable reactor configuration. Suitable configurations may include, butare not limited to, batch reactors, semi-batch reactors, or continuousreactor designs such as, for example, fluidized bed reactors withexternal regeneration vessels. Reactor designs may include, but are notlimited to tubular reactors, fixed bed reactors, or any other reactortype suitable for carrying out the oligomerization reaction. In someembodiments, a continuous oligomerization process for the production ofdiesel and jet fuel boiling range hydrocarbons may be carried out usingan oligomerization reactor for contacting an olefinic feed streamcomprising short chain olefins having a chain length of from 2 to 8carbon atoms with a zeolite catalyst under elevated temperature andpressure so as to convert the short chain olefins to a fuel blend in thediesel boiling range. The oligomerization reactor may be operated atrelatively high pressures of about 20 bar to about 100 bar, andtemperatures ranging between about 150° C. and about 300° C., preferablybetween about 200° C. to 250° C.

The resulting oligomerization stream results in a fuel blend that mayhave a wide variety of products including products comprising C5 to C24hydrocarbons. Additional processing may be used to obtain a fuel blendmeeting a desired standard. An initial separation step may be used togenerate a fuel blend with a narrower range of carbon numbers. In someembodiments, a separation process such as a distillation process may beused to generate a fuel blend comprising C12 to C24 hydrocarbons forfurther processing. The remaining hydrocarbons may be used to produce afuel blend for gasoline, recycled to the oligomerization reactor, orused in additional processes. For example, a kerosene fraction may bederived along with the diesel fraction and may either be used as anilluminating paraffin, as a jet fuel blending component in conventionalcrude or synthetic derived jet fuels, or as reactant (especially C10 toC13 fraction) in the process to produce LAB (Linear Alkyl Benzene). Thenaphtha fraction, after hydroprocessing, may be routed to a thermalcracker for the production of ethylene and propylene or routed to acatalytic cracker to produce ethylene, propylene, and gasoline.

Additional processes may be used to treat the fuel blend to removecertain components or further conform the fuel blend to a diesel or jetfuel standard. Suitable techniques may include hydrotreating to removeany remaining oxygen, sulfur, or nitrogen in the fuel blend.Hydrogenation may be carried after the hydrotreating process to saturateat least some olefinic bonds. Such hydrogenation may be performed toconform the fuel blend to a specific fuel standard (e.g., a diesel fuelstandard or a jet fuel standard). The hydrogenation step of the fuelblend stream may be carried out according to the known procedures, in acontinuous or batchwise manner.

To facilitate a better understanding of the present invention, thefollowing examples are given. In no way should the following examples beread to limit, or to define, the scope of the invention.

EXAMPLES

Unless otherwise indicated below, reactions were conducted in a Parr5000HASTELLOY multireactor unit containing 6×75 mL reactors operated inparallel at pressures up to 135 bar and temperatures up to 275° C.,stirred by magnetic stir bar. Alternate studies were conducted in 100 mLParr 4590 reactors, with mixing by a top-driven stir shaft impeller,which was also capable of attaining a pressure of 135 bar and atemperature of 275° C. Liquid chromatographic analyses were conducted byHPLC using a Bio-Rad Aminex HPX-87H column (300 mm×7.8 mm) at a flowrate of 0.6 mL/min 5 mM sulfuric acid in water and an oven temperatureof 30° C. The run time was 70 minutes.

Gas chromatographic analyses were conducted using a 60 m×0.32 mm ID DB-5column of 1 μm thickness, with 50:1 split ratio, 2 ml/min helium flow,and column oven temperature of 40° C. for 8 minutes, followed by a rampto 285° C. at 10° C./min and a hold time of 53.5 minutes. The injectortemperature was set at 250° C., and the detector temperature was set at300° C.

Example 1 Preparation and Digestion of Cellulosic Biomass Fines

Partially digested cellulosic biomass (cellulosic biomass fines) wasobtained by treating 4.217 grams of softwood (pine) chips in ahydrothermal digestion unit at 191° C. using with 50% 2-propanol/wateras digestion solvent, which was upwardly flowing at a liquid flow rateof 0.20 mL/min, corresponding to an estimated interstitial fluidvelocity of 0.67 ft/hour. As they were formed and fluidized, thecellulosic biomass fines were removed from the packed chip bed (nominal8 mm×8 mm×3 mm) by liquid overflow and collected in a riser tube. Theparticle size was estimated at 10-100 microns via digital imageanalysis.

In a separate experiment, the digestion above was repeated by heatingthe hydrothermal digestion unit at 250° C. for 7 hours using 50%2-propanol/water solvent, buffered via 0.5% sodium carbonate, at anupwardly directed fluid flow rate of 0.2 mL/min. The effluent pH was4.6. Opening of the digestion unit after the heating period revealedfull digestion of the cellulosic biomass originally contained in thedigestion unit with only a small portion of suspended fines remaining.Cellulosic biomass fines were again collected in the riser tube. Lessthan 0.5 grams of cellulosic biomass fines were collected in the risertube, corresponding to less than 10% of the original cellulosic biomasscharge.

Example 2 Use of Cellulosic Biomass Fines to Filter a Slurry Catalyst

As a control experiment, 0.47 grams of a NiMo catalyst on alumina havinga nominal particulate size of 7.7 μm was suspended by shaking in 20 mLof deionized water and charged to a vertical 12.5 inch×0.5 inch O.D.stainless steel tube. A 40 μm in-line filter (Swagelok) was attached tothe bottom of the tube, followed by a metering/shutoff valve directly onthe bottom of the tube. 40 psi air pressure was applied to the top ofthe tube. The metering/shutoff valve was opened to establish a drip ratethrough the filter of approximately 2 drops per second. The filtrate wascollected via a Teledyne/Isco Retriever 500 fraction collector set tocollect fractions every one minute. Fractions were collected for 7minutes, and the amounts of catalyst solids collected from the fractionsare summarized in Table 1. As initially collected, the fractions wereturbid gray, indicating suspension of catalyst. After gravity sewingovernight, the catalyst particulates deposited on the bottom of thevessel, from which the catalyst fraction could be determined via directmeasurement of the catalyst height in enlarged digital images.

TABLE 1 Fraction Mass of Volume Solid Fraction # (mL) (g) 1 3.625 0.00702 2.000 0.0035 3 1.625 0.0035 4 1.438 0.0070 5 1.250 0.0049 6 7.6760.0645 7 2.000 0.0904 total 0.1808 19.6 (38.5%)

The foregoing experiment was repeated with the addition and suspensionof 0.76 grams of cellulosic biomass fines prepared as in Example 1. Incontrast to the control, digital analysis revealed detectable slurrycatalyst only in the first vial, and the total amount of eluted catalystparticulates was only 0.02% of the total catalyst charge. Fractions werecollected for 9 minutes, and the amounts of catalyst solids collectedfrom the fractions are summarized in Table 2. In this case, the sampleswere lightly yellow tinted but translucent, presumably due to solublecomponents leeched from the cellulosic biomass fines. Backflush of thefilter after disassembly enabled recovery of the filtered catalyst.

TABLE 2 Fraction Mass of Volume Solid Fraction # (mL) (g) vial # 3.12500.0035 1 1.0000 0.0000 2 1.0000 0.0000 3 2.2500 0.0000 4 2.5000 0.0000 51.8750 0.0000 6 2.7500 0.0000 7 3.1250 0.0000 8 1.5000 0.0000 9 19.10.0035

Example 3 Digestion of Cellulosic Biomass in the Presence of aBottom-Loaded Slurry Catalyst

The lower 2.25-inch zone of a 12.5 inch×0.5-inch O.D. (0.402-inch I.D)digester tube was packed with ⅛-inch ceramic spheres (Denstone),followed by 0.7-inches of 14×40 mesh filter sand. On the sand was placed0.604 grams of sulfided cobalt molybdate catalyst (DC2534, CriterionCatalyst & Technologies L.P) containing 1-10% cobalt oxide andmolybdenum trioxide (up to 30 wt %) on alumina crushed to a particlesize of less than 100 μm. The catalyst was previously sulfided asdescribed in United States Patent Application publication 20100236988.The tube was then packed with 4.00 grams of southern pine wood chipshaving a nominal dimension of 3 mm×5 mm×5 mm, thereby forming an 8.7inch chip bed.

The digestion unit was filled from the bottom with 50%2-propanol/deionized water, buffered with 0.3 wt % sodium carbonate.Addition of the digestion solvent was continued until void spaces in thechip bed were filled and a liquid layer more than 0.5 inches above thebed was obtained. The ratio of solvent to dry wood in the packed bed wasless than 5.8:1. Liquid flow was then terminated. The digestion unit wasthen pressured to 70 bar with H2, and a continuous flow of hydrogen wasadded from the bottom of the digestion unit and vented from the top at aflow rate of 95 ml/min at standard room temperature and atmosphericpressure (STP). This flow rate corresponded to a superficial linearvelocity of hydrogen flow of 0.05 cm/sec through the digestion unit. Thebottom entry port was tubing having a nominal 3 mm O.D. (2 mm I.D.),thereby acting as a nozzle for gas bubble formation.

The digestion unit was then heated to 190° C. for 1.5 hours, followed byheating to 240° C. for 3.5 hours. At the end of the experiment, 9.24grams of liquid product was drained from the digestion unit. 7.8 gramsof condensed liquid product was also collected from overflow carriedwith the hydrogen sparge. Analysis of the liquid product indicated amixture of oxygenated products (including monohydric alcohols andglycols) at 82% of the expected theoretical yield based on the amount ofcarbohydrates present in the initial wood charge. There were noremaining wood solids at the end of the digestion period.

Example 4 Digestion of Cellulosic Biomass in the Presence of aTop-Loaded Slurry Catalyst

The experiment of Example 3 was repeated, except the 0.600 grams of thecatalyst was placed on top of the chip bed, rather than beneath it. Theinitial ratio of solvent to dry wood was less than 5.5:1. Afterdigestion, 10.1 grams of liquid product was drained from the digestionunit, and 7.28 grams of condensed liquid product was collected fromoverflow. Again, no observable wood solids remained at the end of thedigestion period. In contrast to catalyst loading beneath the chip bed,which produced a relatively high yield, the yield with catalyst loadingon the top of the chip bed produced a yield that was only 28% of thetheoretical yield. LC/MS analysis of the liquid product indicated thepossible presence of oligomeric byproducts having a molecular weightgreater than 300 and too high for detection by gas chromatography.

Example 5 Digestion of Cellulosic Biomass in the Presence of aBottom-Loaded Slurry Catalyst at a Lower Pressure

The experiment of Example 3 was repeated using 6.05 grams of southernpine chips and 15.4 mL of digestion solvent, added from the bottom, tofully cover the chip bed. In this case, the digestion unit waspressurized only to 37 bar, relative to an estimated solvent vaporpressure of about 32 bar. The vented hydrogen flow rate was 97 mL/min,and a digestion solvent of 50% 2-propanol in deionized water was co-fedfrom the bottom of the digestion unit at a flow rate of 0.05 mL/min. Thedigestion unit was heated to 190° C. for 1.5 hours, followed by heatingto 240° C. for 5 hours, with hydrogen and digestion solvent flow ratesmaintained at the same levels. 18.53 grams of liquid product was drainedfrom overflow, and 8.17 grams was drained from the digestion unit at theend of the run. 5.167 grams of wood chips were required to repack thedigestion unit to its previous level. This result indicated a minimum of85% digestion under the digestion conditions. Gas chromatographicanalysis indicated only 31% conversion to the desired products.Comparison of this result with Example 3 showed that increased hydrogenpressure promoted stabilization of the soluble carbohydrates in the formof a higher yield.

Example 6 Digestion of Cellulosic Biomass in the Presence of aBottom-Loaded Slurry Catalyst with No Hydrogen Flow

The experiment of Example 5 was repeated with initial pressurizationwith 70 bar hydrogen, but only maintaining digestion solvent flowthrough the cellulosic biomass and no hydrogen flow. At the end of therun, 17.45 grams of liquid product was drained from overflow, and 7.4grams of liquid product was drained from the digestion unit. 8 ml ofundigested wood was also collected after the run, indicating about 50%conversion. Gas chromatographic analysis indicated about 27% yield ofthe desired reaction product in the liquid product. Again, poorerstabilization occurred when the amount of available hydrogen was reducedby termination of its flow.

Example 7 Digestion of Cellulosic Biomass in the Absence of a SlurryCatalyst

The experiment of Example 3 was repeated after addition of 6.76 grams ofpine chips, but without including the slurry catalyst. Although all thewood charge was digested in 6.5 hours, GC analysis indicated that only3% of the desired reaction product formed.

Example 8 Digestion of Cellulosic Biomass in the Presence of aBottom-Loaded Slurry Catalyst at Room Temperature with Gas and LiquidFlow

The experiment of Example 3 was repeated with the addition of 5.29 gramsof southern pine wood chips, but the digestion unit was maintained at23.5° C. for the duration of exposure. 7.597 grams of liquid product wasdrained from the digestion unit at the end of the run. Analysis of thechip bed following removal of the liquid product indicated uniformdispersal of the catalyst throughout the height of the cellulosicbiomass bed, thereby showing that gas and liquid flow can be effectivefor distributing the slurry catalyst in the cellulosic biomass solids.

Example 9 Digestion of Cellulosic Biomass in the Presence of aBottom-Loaded Slurry Catalyst at Room Temperature with Liquid Flow Only

The experiment of Example 8 was repeated after refilling with 7.13 gramsof pine chips, except upflow of hydrogen was not used and only 0.05mL/min upflow of the digestion solvent was present. 1.36 grams of liquidproduct was drained from overflow and 10.67 grams of liquid product wasobtained from the digestion unit. Analysis of the chip bed followingremoval of the liquid product showed that the catalyst was onlydistributed in approximately the lower 20% of the chip bed, with nocatalyst found distributed in the upper portions of the wood chipcharge.

Example 10 Determination of Minimum Gas Velocity Needed for Fluidizationof Slurry Catalyst

A 100 mL graduated cylinder was filled with 1 gram of nominal 1-25 μmNiMo/alumina slurry catalyst and 50 grams of deionized water. A frittedsparging stone (ACE Glass) was placed at the bottom of the graduatedcylinder and connected to an N₂ supply using ⅛-inch Teflon tubing. TheN₂ flow rate was varied to determine minimum flow rate needed tocompletely fluidize the slurry catalyst to the top of the liquid column.The linear velocity of gas corresponding to complete fluidizationdetermined using this method was 0.037 cm/sec. Hydrogen gas flow, whenused in the previous examples, exceeded this minimum velocity forfluidization and suspension of the catalyst.

Example 11 Paste Formation at High Loadings of Cellulosic Biomass Solids

2.08 grams of finely ground pine wood sawdust containing 11.3% moisturewas added to 25.5 grams of deionized water in a graduated cylinder.After mixing and allowing the wood to equilibrate, 10.4 grams of waterwas removed by syringe from the top of the wood bed. The cylinder wasthen tilted to decant additional water, but only one gram of additionalwater was removed, yielding a final water to dry solids ratio of 8.3:1.0.1 grams of a slurry catalyst having a particle size of 1-25 micronswas added, and the cylinder was mixed by inverting several times.Virtually no mixing of the slurry catalyst with the wood was observeddue to paste formation by the finely divided wood.

Example 12 Role of Biomass Particulate Size on Digestion Rate

Parallel Parr 5000 reactors were loaded with 20.0 grams of 50%2-propanol in deionized water containing 0.05 grams of sodium carbonate.2.70 grams of soft wood pine chips containing 39% moisture was added toeach reactor. In the first reactor, a single 1 inch×1 inch×3 mm woodchip was added. In the second reactor, the pine wood was hand clipped toseveral ¼ inch×¼ inch×3 mm mini chips. In the third reactor, the pinewood was ground in a coffee grinder to a nominal 3 mm maximum size.

All three reactors were pressurized to 51 bar with H₂ and heated to 190°C. for one hour before ramping to 240° C. to complete a 5 hour cycle.The reactor contents were filtered by Whatman GF/F filter paper, and thepaper with solids was dried in a vacuum oven overnight at 90° C. 78% byweight of wood from the first reactor dissolved, and the smaller woodchips in the other two reactors gave 72% by weight dissolution, on awater-free basis. It is believed that these results are essentially thesame within experimental error and that the digestion rate is notsignificantly impacted by the wood chip size.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. The invention illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods may also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

We claim:
 1. A method comprising: providing cellulosic biomass solidsand a slurry catalyst in a hydrothermal digestion unit, the slurrycatalyst being capable of activating molecular hydrogen; providing adigestible filter aid in the hydrothermal digestion unit; distributingthe slurry catalyst within the cellulosic biomass solids using fluidflow; retaining at least a portion of the slurry catalyst in a fixedlocation using the digestible filter aid; heating the cellulosic biomasssolids in the hydrothermal digestion unit in the presence of the slurrycatalyst, a digestion solvent, and molecular hydrogen, thereby forming aliquor phase comprising soluble carbohydrates; and performing a firstcatalytic reduction reaction on the soluble carbohydrates within thehydrothermal digestion unit, thereby at least partially forming areaction product comprising a triol, a diol, a monohydric alcohol, orany combination thereof in the hydrothermal digestion unit.
 2. Themethod of claim 1, further comprising: allowing a portion of the liquorphase to exit the hydrothermal digestion unit; forming a filter cakecomprising the digestible filter aid on a solids retention mechanismconfigured to allow the liquor phase to pass therethrough; andcollecting at least a portion of the slurry catalyst on the filter cake.3. The method of claim 2, wherein the solids retention mechanismcomprises a filter that is within the hydrothermal digestion unit. 4.The method of claim 2, wherein the solids retention mechanism comprisesa filter that is external to the hydrothermal digestion unit.
 5. Themethod of claim 2, further comprising: removing the filter cake from thesolids retention mechanism; and returning at least a portion of theslurry catalyst to the cellulosic biomass solids.
 6. The method of claim2, wherein at least a portion of the digestible filter aid isdistributed in the cellulosic biomass solids and promotes retention ofthe slurry catalyst therein.
 7. The method of claim 2, furthercomprising: performing a second catalytic reduction reaction on theliquor phase that has exited the hydrothermal digestion unit so as tofurther form the reaction product.
 8. The method of claim 1, furthercomprising: dissolving at least a portion of the digestible filter aidwhile forming fresh digestible filter aid, the fresh digestible filteraid comprising cellulosic biomass particulates with a particulate sizeof at most about 3 mm that are formed by heating the cellulosic biomasssolids in the presence of the digestion solvent.
 9. The method of claim1, wherein the digestible filter aid comprises cellulosic biomassparticulates with a particulate size of at most about 3 mm.
 10. Themethod of claim 1, wherein the slurry catalyst is provided in thehydrothermal digestion unit before the cellulosic biomass solids areprovided.
 11. The method of claim 1, wherein providing the digestiblefilter aid in the hydrothermal digestion unit comprises adding thedigestible filter aid to the hydrothermal digestion unit.
 12. The methodof claim 11, wherein the digestible filter aid is added to thehydrothermal digestion unit with the cellulosic biomass solids.
 13. Themethod of claim 1, wherein providing the digestible filter aid comprisesforming the digestible filter aid in the hydrothermal digestion unit byheating the cellulosic biomass solids in the presence of the digestionsolvent.
 14. The method of claim 13, further comprising: adding anadditional quantity of the digestible filter aid to the hydrothermaldigestion unit while the digestible filter aid is being formed therein.15. The method of claim 13, wherein the digestible filter aid comprisescellulosic biomass particulates with a particulate size of at most about3 mm that are formed by heating the cellulosic biomass solids in thepresence of the digestion solvent.
 16. The method of claim 1, whereinthe slurry catalyst is distributed in the cellulosic biomass solidsusing upwardly directed fluid flow.
 17. The method of claim 16, whereinthe upwardly directed fluid flow comprises one or more upwardly directedfluid streams, the one or more upwardly directed fluid streamscomprising a gas stream, a liquid stream, or any combination thereof.18. The method of claim 1, wherein the digestion solvent comprises thereaction product.
 19. The method of claim 1, further comprising:converting the reaction product into a biofuel.
 20. The method of claim1, wherein the slurry catalyst comprises a poison-tolerant catalyst. 21.A method comprising: providing cellulosic biomass solids and a slurrycatalyst in a hydrothermal digestion unit, the slurry catalyst beingcapable of activating molecular hydrogen and the cellulosic biomasssolids comprising a digestible filter aid comprising cellulosic biomassparticulates capable of forming a filter cake suitable for retaining atleast a portion of the slurry catalyst thereon; distributing the slurrycatalyst within the cellulosic biomass solids using upwardly directedfluid flow; heating the cellulosic biomass solids in the hydrothermaldigestion unit in the presence of the slurry catalyst, a digestionsolvent, and molecular hydrogen, thereby forming a liquor phasecomprising soluble carbohydrates; allowing a portion of the liquor phaseto exit the hydrothermal digestion unit; forming a filter cakecomprising the digestible filter aid on a solids retention mechanismconfigured to allow the liquor phase to pass therethrough; collecting atleast a portion of the slurry catalyst on the filter cake; andperforming a first catalytic reduction reaction on the solublecarbohydrates within the hydrothermal digestion unit, thereby at leastpartially forming a reaction product comprising a triol, a diol, amonohydric alcohol, or any combination thereof in the hydrothermaldigestion unit.
 22. The method of claim 21, wherein the solids retentionmechanism comprises a filter that is within the hydrothermal digestionunit.
 23. The method of claim 21, wherein the solids retention mechanismcomprises a filter that is external to the hydrothermal digestion unit.24. The method of claim 21, further comprising: removing the filter cakefrom the solids retention mechanism; and returning at least a portion ofthe slurry catalyst to the cellulosic biomass solids.
 25. The method ofclaim 21, wherein at least a portion of the digestible filter aid isdistributed in the cellulosic biomass solids and promotes retention ofthe slurry catalyst therein.
 26. The method of claim 21, furthercomprising: performing a second catalytic reduction reaction on theliquor phase that has exited the hydrothermal digestion unit so as tofurther form the reaction product.
 27. The method of claim 21, whereinthe cellulosic biomass particulates have a particulate size of at mostabout 3 mm.
 28. The method of claim 21, wherein the digestible filteraid is added to the hydrothermal digestion unit.
 29. The method of claim28, wherein the digestible filter aid is mixed with the cellulosicbiomass solids before the cellulosic biomass solids are provided in thehydrothermal digestion unit.
 30. The method of claim 21, wherein thedigestible filter aid is formed in the hydrothermal digestion unit byheating the cellulosic biomass solids in the presence of the digestionsolvent.
 31. The method of claim 30, further comprising: adding anadditional quantity of the digestible filter aid to the hydrothermaldigestion unit while the digestible filter aid is being formed therein.32. The method of claim 21, wherein the upwardly directed fluid flowcomprises one or more upwardly directed fluid streams, the one or moreupwardly directed fluid streams comprising a gas stream, a liquidstream, or any combination thereof.
 33. The method of claim 21, furthercomprising: dissolving at least a portion of the digestible filter aidwhile forming fresh digestible filter aid, the fresh digestible filteraid comprising cellulosic biomass particulates with a particulate sizeof at most about 3 mm that are formed by heating the cellulosic biomasssolids in the presence of the digestion solvent.
 34. The method of claim21, wherein the slurry catalyst is provided in the hydrothermaldigestion unit before the cellulosic biomass solids are provided. 35.The method of claim 21, wherein the digestion solvent comprises thereaction product.
 36. The method of claim 21, further comprising:converting the reaction product into a biofuel.
 37. The method of claim21, wherein the slurry catalyst comprises a poison-tolerant catalyst.